diff --git a/lang/en/lang.php b/lang/en/lang.php
--- a/lang/en/lang.php
+++ b/lang/en/lang.php
@@ -1,34 +1,38 @@
 <?php
 $lang['created_by_davcal'] = 'Created by DAVCal for DokuWiki';
 $lang['unknown_error'] = 'Unknown Error';
 $lang['event_added'] = 'Event added';
 $lang['event_edited'] = 'Event edited';
 $lang['event_deleted'] = 'Event deleted';
 $lang['no_permission'] = 'You don\'t have permission to modify this calendar';
 $lang['settings'] = 'Settings/Sync';
 $lang['settings_saved'] = 'Settings saved successfully';
 $lang['error_saving'] = 'Error saving settings.';
 $lang['local_time'] = 'Local time (Browser based)';
 $lang['js']['create_new_event'] = 'Create new Event';
 $lang['js']['cancel'] = 'Cancel';
 $lang['js']['create'] = 'Create';
 $lang['js']['save'] = 'Save';
 $lang['js']['settings'] = 'Settings';
 $lang['js']['edit'] = 'Edit';
 $lang['js']['delete'] = 'Delete';
 $lang['js']['edit_event'] = 'Edit Event';
 $lang['js']['allday'] = 'All Day Event';
 $lang['js']['title'] = 'Title';
 $lang['js']['from'] = 'From';
 $lang['js']['to'] = 'To';
 $lang['js']['yes'] = 'Yes';
 $lang['js']['confirmation'] = 'Confirmation';
 $lang['js']['ok'] = 'OK';
 $lang['js']['info'] = 'Info';
 $lang['js']['really_delete_this_event'] = 'Really delete this event?';
 $lang['js']['timezone'] = 'Timezone';
 $lang['js']['weeknumbers'] = 'Week Numbers';
 $lang['js']['use_lang_tz'] = 'Use Timezone from language setting';
 $lang['js']['only_workweek'] = 'Show only Work Week';
 $lang['js']['sync_url'] = 'DAVCal URL';
 $lang['js']['error_retrieving_data'] = 'There was an error retrieving data from the calendar server.';
+$lang['js']['start_date_invalid'] = 'Start date/time is invalid.';
+$lang['js']['end_date_invalid'] = 'End date/time is invalid.';
+$lang['js']['end_date_before_start_date'] = 'End date/time is before start date/time.';
+$lang['js']['end_date_is_same_as_start_date'] = 'End date/time is equal to start date/time.';
diff --git a/script.js b/script.js
--- a/script.js
+++ b/script.js
@@ -1,478 +1,516 @@
 /* DOKUWIKI:include_once fullcalendar-2.4.0/moment.js */
 /* DOKUWIKI:include_once fullcalendar-2.4.0/fullcalendar.js */
 /* DOKUWIKI:include_once fullcalendar-2.4.0/lang/de.js */
 /* DOKUWIKI:include_once fullcalendar-2.4.0/lang/en.js */
 /* DOKUWIKI:include_once datetimepicker-2.4.5/jquery.datetimepicker.js */
 
 jQuery(function() {
     // Redefine functions for using moment.js with datetimepicker
     
     Date.parseDate = function( input, format ){
       return moment(input,format).toDate();
     };
     Date.prototype.dateFormat = function( format ){
       return moment(this).format(format);
     };
     
     // Attach to event links
     
     jQuery('div.fullCalendarSettings a').each(function() {
         var $link = jQuery(this);
         var href = $link.attr('href');
         if (!href) return;
         
         $link.click(
             function(e) {
                 dw_davcal__modals.showSettingsDialog();
                 e.preventDefault();
                 return '';
             }
         );
         }
     );
     
     var postArray = { };
     jQuery.post(
         DOKU_BASE + 'lib/exe/ajax.php',
         {
             call: 'plugin_davcal',
             id: JSINFO.id,
             action: 'getSettings',
             params: postArray
         },
         function(data)
         {
             var result = data['result'];
             if(result === true)
             {
                 dw_davcal__modals.settings = data['settings'];
                 var wknum = false;
                 var tz = false;
                 var we = true;
                 if(data['settings']['weeknumbers'] == 1)
                     wknum = true;
                 if(data['settings']['timezone'] !== '')
                     tz = data['settings']['timezone'];
                 if(data['settings']['workweek'] == 1)
                     we = false;
                 // Initialize the davcal popup
                 var res = jQuery('#fullCalendar').fullCalendar({
                     dayClick: function(date, jsEvent, view) {
                         dw_davcal__modals.showEditEventDialog(date, false);
                     },
                     eventClick: function(calEvent, jsEvent, view) {
                         dw_davcal__modals.showEditEventDialog(calEvent, true);
                     },
                     events: {
                         url: DOKU_BASE + 'lib/exe/ajax.php',
                         type: 'POST',
                         data: {
                             call: 'plugin_davcal',
                             action: 'getEvents',
                             id: JSINFO.id
                         },
                         error: function() {
                             dw_davcal__modals.msg = LANG.plugins.davcal['error_retrieving_data'];
                             dw_davcal__modals.showDialog(false);
                         }
                     },
                     header: {
                         left: 'title',
                         center: 'today prev,next',
                         right: 'month,agendaWeek,agendaDay'
                     },
                     lang: JSINFO.plugin.davcal['language'],
                     weekNumbers: wknum,
                     timezone: tz,
                     weekends: we,
                 });
             }
         }
     );    
 });
 
 var dw_davcal__modals = {
     $editEventDialog: null,
     $dialog: null,
     $settingsDialog: null,
     msg: null,
     completeCb: null,
     action: null,
     uid: null,
     settings: null,
     
     showSettingsDialog : function() {
         if(dw_davcal__modals.$settingsDialog)
             return;
 
         var dialogButtons = {};
         dialogButtons[LANG.plugins.davcal['save']] = function() {
             var postArray = { };
             jQuery("input[class=dw_davcal__settings], select[class=dw_davcal__settings]").each(function() {
               if(jQuery(this).attr('type') == 'checkbox')
               {
                   postArray[jQuery(this).prop('name')] = jQuery(this).prop('checked') ? 1 : 0;
               }
               else
               {
                   postArray[jQuery(this).prop('name')] = jQuery(this).val();
               }
             });
             jQuery('#dw_davcal__ajaxsettings').html('<img src="'+DOKU_BASE+'lib/images/throbber.gif" alt="" width="16" height="16" />');
             jQuery.post(
                 DOKU_BASE + 'lib/exe/ajax.php',
                 {
                     call: 'plugin_davcal',
                     id: JSINFO.id,
                     action: 'saveSettings',
                     params: postArray
                 },
                 function(data)
                 {
                     var result = data['result'];
                     var html = data['html'];
                     jQuery('#dw_davcal__ajaxsettings').html(html);
                     if(result === true)
                     {
                         location.reload();
                     }
                 }
             );
         };
         dialogButtons[LANG.plugins.davcal['cancel']] = function () {
             dw_davcal__modals.hideSettingsDialog();
         };
         
         dw_davcal__modals.$settingsDialog = jQuery(document.createElement('div'))
        .dialog({
            autoOpen: false,
            draggable: true,
            title: LANG.plugins.davcal['settings'],
            resizable: true,         
            buttons: dialogButtons,
        })
        .html(
             '<div><table>' +
             //'<tr><td>' + LANG.plugins.davcal['use_lang_tz'] + '</td><td><input type="checkbox" name="use_lang_tz" id="dw_davcal__settings_use_lang_tz" class="dw_davcal__settings"></td></tr>' + 
             '<tr><td>' + LANG.plugins.davcal['timezone'] + '</td><td><select name="timezone" id="dw_davcal__settings_timezone" class="dw_davcal__settings"></select></td></tr>' +
             '<tr><td>' + LANG.plugins.davcal['weeknumbers'] + '</td><td><input type="checkbox" name="weeknumbers" id="dw_davcal__settings_weeknumbers" class="dw_davcal__settings"></td></tr>' +
             '<tr><td>' + LANG.plugins.davcal['only_workweek'] + '</td><td><input type="checkbox" name="workweek" id="dw_davcal__settings_workweek" class="dw_davcal__settings"></td></tr>' +
             '<tr><td>' + LANG.plugins.davcal['sync_url'] + '</td><td><input type="text" name="syncurl" readonly="readonly" value="' + dw_davcal__modals.settings['syncurl'] + '"></td></tr>' + 
             '</table>' +
             '</div>' +
             '<div id="dw_davcal__ajaxsettings"></div>'
             )
        .parent()
        .attr('id','dw_davcal__settings')
        .show()
        .appendTo('.dokuwiki:first');
        
            // attach event handlers
         jQuery('#dw_davcal__settings .ui-dialog-titlebar-close').click(function(){
           dw_davcal__modals.hideSettingsDialog();
         });
         
         var $tzdropdown = jQuery('#dw_davcal__settings_timezone');
         jQuery('#fullCalendarTimezoneList option').each(function() {
             jQuery('<option />', {value: jQuery(this).val(), 
                     text: jQuery(this).text()}).appendTo($tzdropdown);
         });
         
         if(dw_davcal__modals.settings)
         {
             if(dw_davcal__modals.settings['timezone'] !== '')
                 jQuery('#dw_davcal__settings_timezone').val(dw_davcal__modals.settings['timezone']);
             if(dw_davcal__modals.settings['weeknumbers'] == 1)
                 jQuery('#dw_davcal__settings_weeknumbers').prop('checked', true);
             else
                 jQuery('#dw_davcal__settings_weeknumbers').prop('checked', false);
                 
             if(dw_davcal__modals.settings['workweek'] == 1)
                 jQuery('#dw_davcal__settings_workweek').prop('checked', true);
             else
                 jQuery('#dw_davcal__settings_workweek').prop('checked', false);
         }        
     },
     
+    checkEvents : function() {
+        var allDay = jQuery('#dw_davcal__allday_edit').prop('checked');
+        var startDate = moment(jQuery('#dw_davcal__eventfrom_edit').val(), 'YYYY-MM-DD');
+        var endDate = moment(jQuery('#dw_davcal__eventto_edit').val(), 'YYYY-MM-DD');
+        if(!allDay)
+        {
+            var startTime = moment.duration(jQuery('#dw_davcal__eventfromtime_edit').val());
+            var endTime = moment.duration(jQuery('#dw_davcal__eventtotime_edit').val());
+            startDate.add(startTime);
+            endDate.add(endTime);
+        }
+        if(!startDate.isValid())
+        {
+            dw_davcal__modals.msg = LANG.plugins.davcal['start_date_invalid'];
+            dw_davcal__modals.showDialog(false);
+            return false;
+        }
+        if(!endDate.isValid())
+        {
+            dw_davcal__modals.msg = LANG.plugins.davcal['end_date_invalid'];
+            dw_davcal__modals.showDialog(false);
+            return false;
+        }
+        if(endDate.isBefore(startDate))
+        {
+            dw_davcal__modals.msg = LANG.plugins.davcal['end_date_before_start_date'];
+            dw_davcal__modals.showDialog(false);
+            return false;
+        }
+        if(!allDay && endDate.isSame(startDate))
+        {
+            dw_davcal__modals.msg = LANG.plugins.davcal['end_date_is_same_as_start_date'];
+            dw_davcal__modals.showDialog(false);
+            return false;
+        }
+        return true;
+    },
+    
     showEditEventDialog : function(event, edit) {
         if(dw_davcal__modals.$editEventDialog)
             return;
          
         var title = '';   
         var dialogButtons = {};
         var calEvent = [];
         if(edit)
         {
             calEvent = event;
             title = LANG.plugins.davcal['edit_event'];
             dialogButtons[LANG.plugins.davcal['edit']] = function() {
                 if(!dw_davcal__modals.checkEvents())
                   return;
                 var postArray = { };
                 jQuery("input.dw_davcal__editevent").each(function() {
                   if(jQuery(this).attr('type') == 'checkbox')
                   {
                       postArray[jQuery(this).prop('name')] = jQuery(this).prop('checked') ? 1 : 0;
                   }
                   else
                   {
                       postArray[jQuery(this).prop('name')] = jQuery(this).val();
                   }
                 });
                 jQuery('#dw_davcal__ajaxedit').html('<img src="'+DOKU_BASE+'lib/images/throbber.gif" alt="" width="16" height="16" />');
                 jQuery.post(
                     DOKU_BASE + 'lib/exe/ajax.php',
                     {
                         call: 'plugin_davcal',
                         id: JSINFO.id,
                         action: 'editEvent',
                         params: postArray
                     },
                     function(data)
                     {
                         var result = data['result'];
                         var html = data['html'];
                         jQuery('#dw_davcal__ajaxedit').html(html);
                         if(result === true)
                         {
                             jQuery('#fullCalendar').fullCalendar('refetchEvents');
                             dw_davcal__modals.hideEditEventDialog();
                         }
                     }
                 );
             };
             dialogButtons[LANG.plugins.davcal['delete']] = function() {
                 dw_davcal__modals.action = 'deleteEvent';
                 dw_davcal__modals.msg = LANG.plugins.davcal['really_delete_this_event'];
                 dw_davcal__modals.completeCb = function(data) {
                     if(data.result == false)
                     {
                         dw_davcal__modals.msg = data.errmsg;
                         dw_davcal__modals.showDialog(false);
                     }
                     else
                     {
                         jQuery('#fullCalendar').fullCalendar('refetchEvents');
                         dw_davcal__modals.hideEditEventDialog();
                     }
                 };
                 dw_davcal__modals.showDialog(true);
             };
         }
         else
         {
             calEvent.start = event;
             calEvent.end = moment(event);
             calEvent.start.hour(12);
             calEvent.start.minute(0);
             calEvent.end.hour(13);
             calEvent.end.minute(0);
             calEvent.allDay = false;
             calEvent.title = '';
             calEvent.id = '0';
             title = LANG.plugins.davcal['create_new_event'];
             dialogButtons[LANG.plugins.davcal['create']] = function() {
                 if(!dw_davcal__modals.checkEvents())
                   return;
 
                 var postArray = { };
                 jQuery("input.dw_davcal__editevent").each(function() {
                   if(jQuery(this).attr('type') == 'checkbox')
                   {
                       postArray[jQuery(this).prop('name')] = jQuery(this).prop('checked') ? 1 : 0;
                   }
                   else
                   {
                       postArray[jQuery(this).prop('name')] = jQuery(this).val();
                   }
                 });
                 jQuery('#dw_davcal__ajaxnew').html('<img src="'+DOKU_BASE+'lib/images/throbber.gif" alt="" width="16" height="16" />');
                 jQuery.post(
                     DOKU_BASE + 'lib/exe/ajax.php',
                     {
                         call: 'plugin_davcal',
                         id: JSINFO.id,
                         action: 'newEvent',
                         params: postArray
                     },
                     function(data)
                     {
                         var result = data['result'];
                         var html = data['html'];
                         jQuery('#dw_davcal__ajaxedit').html(html);
                         if(result === true)
                         {
                             jQuery('#fullCalendar').fullCalendar('refetchEvents');
                             dw_davcal__modals.hideEditEventDialog();
                         }
                     }
                 );
             };
         }
         dialogButtons[LANG.plugins.davcal['cancel']] = function() {
             dw_davcal__modals.hideEditEventDialog();
         };
         dw_davcal__modals.uid = calEvent.id;
         dw_davcal__modals.$editEventDialog = jQuery(document.createElement('div'))
        .dialog({
            autoOpen: false,
            draggable: true,
            title: title,
            resizable: true,         
            buttons: dialogButtons,
        })
        .html(
             '<div><table><tr><td>' + LANG.plugins.davcal['title'] + '</td><td><input type="text" id="dw_davcal__eventname_edit" name="eventname" class="dw_davcal__editevent"></td></tr>' +
             '<tr><td>' + LANG.plugins.davcal['from'] + '</td><td><input type="text" name="eventfrom" id="dw_davcal__eventfrom_edit" class="dw_davcal__editevent dw_davcal__date"><input type="text" name="eventfromtime" id="dw_davcal__eventfromtime_edit" class="dw_davcal__editevent dw_davcal__time"></td></tr>' +
             '<tr><td>' + LANG.plugins.davcal['to'] + '</td><td><input type="text" name="eventto" id="dw_davcal__eventto_edit" class="dw_davcal__editevent dw_davcal__date"><input type="text" name="eventtotime" id="dw_davcal__eventtotime_edit" class="dw_davcal__editevent dw_davcal__time"></td></tr>' +
             '<tr><td colspan="2"><input type="checkbox" name="allday" id="dw_davcal__allday_edit" class="dw_davcal__editevent">' + LANG.plugins.davcal['allday'] + '</td></tr>' +
             '</table>' +
             '<input type="hidden" name="uid" id="dw_davcal__uid_edit" class="dw_davcal__editevent">' +
             '</div>' +
             '<div id="dw_davcal__ajaxedit"></div>'
             )
        .parent()
        .attr('id','dw_davcal__edit')
        .show()
        .appendTo('.dokuwiki:first');
        
        jQuery('#dw_davcal__uid_edit').val(calEvent.id);
        jQuery('#dw_davcal__eventname_edit').val(calEvent.title);
        jQuery('#dw_davcal__eventfrom_edit').val(calEvent.start.format('YYYY-MM-DD'));
        jQuery('#dw_davcal__eventfromtime_edit').val(calEvent.start.format('HH:mm'));
        if(calEvent.allDay && (calEvent.end === null))
        {
            jQuery('#dw_davcal__eventto_edit').val(calEvent.start.format('YYYY-MM-DD'));
            jQuery('#dw_davcal__eventtotime_edit').val(calEvent.start.format('HH:mm'));
        }
        else if(calEvent.allDay)
        {
            endEvent = moment(calEvent.end);
            endEvent.subtract(1, 'days');
            jQuery('#dw_davcal__eventto_edit').val(endEvent.format('YYYY-MM-DD'));
            jQuery('#dw_davcal__eventotime_edit').val(endEvent.format('HH:mm'));
        }
        else
        {
            jQuery('#dw_davcal__eventto_edit').val(calEvent.end.format('YYYY-MM-DD'));
            jQuery('#dw_davcal__eventtotime_edit').val(calEvent.end.format('HH:mm'));
        }
        jQuery('#dw_davcal__allday_edit').prop('checked', calEvent.allDay);
        
            // attach event handlers
         jQuery('#dw_davcal__edit .ui-dialog-titlebar-close').click(function(){
           dw_davcal__modals.hideEditEventDialog();
         });
         jQuery('#dw_davcal__eventfrom_edit').datetimepicker({format:'YYYY-MM-DD',
                                                       formatDate:'YYYY-MM-DD',
                                                       datepicker: true,
                                                       timepicker: false,
                                                       });
         jQuery('#dw_davcal__eventfromtime_edit').datetimepicker({format:'HH:mm',
                                                       formatTime:'HH:mm',
                                                       datepicker: false,
                                                       timepicker: true,
                                                       step: 15});
         jQuery('#dw_davcal__eventto_edit').datetimepicker({format:'YYYY-MM-DD',
                                                       formatDate:'YYYY-MM-DD',
                                                       datepicker: true,
                                                       timepicker: false,
                                                       });
         jQuery('#dw_davcal__eventtotime_edit').datetimepicker({format:'HH:mm',
                                                       formatTime:'HH:mm',
                                                       datepicker: false,
                                                       timepicker: true,
                                                       step:15});
         jQuery('#dw_davcal__allday_edit').change(function() {
             if(jQuery(this).is(":checked"))
             {
                 jQuery('#dw_davcal__eventfromtime_edit').prop('readonly', true);
                 jQuery('#dw_davcal__eventtotime_edit').prop('readonly', true);
             }
             else
             {
                 jQuery('#dw_davcal__eventfromtime_edit').prop('readonly', false);
                 jQuery('#dw_davcal__eventtotime_edit').prop('readonly', false);
             }
         });
         jQuery('#dw_davcal__allday_edit').change();
     },
     
     showDialog : function(confirm)
     {
         if(dw_davcal__modals.$confirmDialog)
             return;
         var dialogButtons = {};
         var title = '';
         if(confirm)
         {
             title = LANG.plugins.davcal['confirmation'];
             dialogButtons[LANG.plugins.davcal['yes']] =  function() {
                             jQuery.post(
                                 DOKU_BASE + 'lib/exe/ajax.php',
                                 {
                                     call: 'plugin_davcal',
                                     id: JSINFO.id,
                                     action: dw_davcal__modals.action,
                                     params: {
                                         uid: dw_davcal__modals.uid
                                     }
                                 },
                                 function(data)
                                 {
                                     dw_davcal__modals.completeCb(data);
                                 }
                             );
                             dw_davcal__modals.hideDialog();
                     };
             dialogButtons[LANG.plugins.tagrevisions['cancel']] = function() {
                             dw_davcal__modals.hideDialog();
                     };
         }
         else
         {
             title = LANG.plugins.davcal['info'];
             dialogButtons[LANG.plugins.davcal['ok']] = function() {
                  dw_davcal__modals.hideDialog();
             };
         }
         dw_davcal__modals.$dialog = jQuery(document.createElement('div'))
             .dialog({
                 autoOpen: false,
                 draggable: true,
                 title: title,
                 resizable: true,
                 buttons: dialogButtons,
             })
             .html(
                 '<div>' + dw_davcal__modals.msg + '</div>'
             )
             .parent()
             .attr('id','dw_davcal__confirm')
             .show()
             .appendTo('.dokuwiki:first');
    
                  // attach event handlers
             jQuery('#dw_davcal__confirm .ui-dialog-titlebar-close').click(function(){
                 dw_davcal__modals.hideDialog();
             });
     },
     
     hideEditEventDialog : function() {
         dw_davcal__modals.$editEventDialog.empty();
         dw_davcal__modals.$editEventDialog.remove();
         dw_davcal__modals.$editEventDialog = null;
     },
     
     hideDialog: function() {
         dw_davcal__modals.$dialog.empty();
         dw_davcal__modals.$dialog.remove();
         dw_davcal__modals.$dialog = null;
     },
     
     hideSettingsDialog: function() {
         dw_davcal__modals.$settingsDialog.empty();
         dw_davcal__modals.$settingsDialog.remove();
         dw_davcal__modals.$settingsDialog = null;
     }
 };