Hi all,

I have a visualforce page that is enabled for Classic and Salesforce 1, it works perfectly on Classic, but occassionally our engineers are reporting they get at error when trying to load the page, or when clicking on one of the record links within the page.
I am also using Adam Shaw's Full Scheduler Calendar.

The errors are:
net:err_blocked_by-_Resource
and
error parsing json response 'Unexpected token <' logged in? undefined

As it's an intermitent issue, I cannot seem to debug it at all. I was wondering if anyone could offer any insight into the errors?
My code is below.
 

<apex:page controller="UserCalendarController" readOnly="true" >
    <link href="{!$Resource.fullBasicCalendarMinCSS}" rel="stylesheet" />
    <link href="{!$Resource.fullBasicCalendarPrintMinCSS}" rel="stylesheet" media="print" />
    
    <script src="//ajax.googleapis.com/ajax/libs/jquery/1.10.1/jquery.min.js"></script>
    <script src="//ajax.googleapis.com/ajax/libs/jqueryui/1.10.3/jquery-ui.min.js"></script>
    <script src="{!$Resource.MomentMin}"></script>
    <script src="{!$Resource.fullBasicCalendarMinJS}"></script>
    <script>
    var WOTag = '{!WOTag}';
    var PHTag = '{!PHTag}';
    var PSTag = '{!PSTag}';
    var TOINFINITY = moment().add(10, "days");
    var TODAY = moment().add(1, "days");
    var NOW = moment();
    window.$userId = "{!$User.Id}";
    
    function htmlEncode(value)
    {
        return $('<div/>').html(value).text();
    }
    
    function newLineToBR(value)
    {
        return value.replace(/(\n)+/g, '<br />'); 
    }
    
    $(document).ready(function() 
                      {
                          //Call the fullCallendar method. 
                          $('#calendar').fullCalendar(
                              {
                                  schedulerLicenseKey: '0760513013-fcs-1521451920',
                                  editable: false,
                                  aspectRatio: 0.75,
                                  eventOrder: 'displayOrder',
                                  eventRender: function (event, element, view) 
                                  {
                                      var title = element.find('.fc-title, .fc-list-item-title');   
                                      var titleNode = title[0].childNodes[0];
                                      var encoded = htmlEncode(titleNode.innerHTML);
                                      titleNode.innerHTML = encoded;
                                     //title.html(title.text());
                                  },
                                  eventMouseover: function(calEvent, jsEvent) 
                                  {
                                      var tooltip = '';
                                      if (calEvent.tag == WOTag)
                                      {
                                          tooltip = '<div class=" tooltipevent WO-tooltipevent">'
                                          + calEvent.toolTipTitle +'<h3><br/>' + calEvent.toolTipContent + '<br/>'
                                          + '</div>';
                                      }
                                      else if (calEvent.tag == PHTag)
                                      {
                                          tooltip = '<div class="tooltipevent PH-tooltipevent">'
                                          + '<h3>' + calEvent.toolTipTitle +'<h3><br/>' + calEvent.toolTipContent + '<br/>'
                                          + '</div>';
                                      }
                                          else if (calEvent.tag == PSTag)
                                          {
                                              tooltip = '<div class="tooltipevent PS-tooltipevent">'
                                              + calEvent.toolTipTitle +'<h3><br/>' + calEvent.toolTipContent + '<br/>'
                                              + '</div>';
                                          }
                                      
                                      $("body").append(tooltip);
                                      $(this).mousemove(function(e) 
                                                        {
                                                            $('.tooltipevent').css('top', e.pageY + 1);
                                                            $('.tooltipevent').css('left', e.pageX + 2);
                                                        });
                                  },                                 
                                  eventMouseout: function(calEvent, jsEvent) 
                                  {
                                      $(this).css('z-index', 8);
                                      $('.tooltipevent').remove();
                                  }, 
                                  eventClick: function(calEvent)
                                  {
                                     /* alert('Event url: ' + calEvent.url);
                                      if (calEvent.url)
                                      {
                                          window.open(calEvent.url, '_parent');
                                          return false;
                                      }*/
                                  },
                                  header: 
                                  {
                                      left: 'prev,next today',
                                      center: 'title',
                                      right: 'listToday, listNext10Days, month'
                                  },
                                  defaultView: 'listToday',
                                  views: 
                                  {             
                                      month: 
                                      {
                                          weekends: false,
                                          fixedWeekCount: false,
                                          buttonText: 'Month'
                                      },
                                      listNext10Days:
                                      {
                                          type: 'list',
                                          duration: {days:TOINFINITY.diff(NOW, 'days')},
                                          buttonText: 'Next 10 days',
                                          weekends: false,
                                          displayEventTime: false
                                      },
                                      listToday:
                                      {
                                          type: 'list',
                                          duration: {days:TODAY.diff(NOW, 'days')},
                                          buttonText: 'Today',
                                          weekends: false,
                                          displayEventTime: false
                                      }
                                  },
                                  events: function(start, end, timezone, callback)
                                  {
                                      console.log('Getting events for ' + start.toDate() + ' - ' + end.toDate());
                                      $('.loader').toggle();
                                      Visualforce.remoting.Manager.invokeAction(
                                          '{!$RemoteAction.UserCalendarController.CalendarEvents}',
                                          start.toDate().toUTCString(),
                                          end.toDate().toUTCString(),
                                          function(result, event)
                                          {
                                              if (event.status)
                                              {
                                                  for (var i = 0; i < result.length; i++)
                                                  {
                                                      var r= result[i];
                                                      r.start = new Date(r.starts);
                                                      r.end = new Date(r.ends);
                                                      //r.toolTipContent = r.toolTipContent.replace(/(\n)+/g, '<br />');
                                                      //r.title = r.title.replace(/(\n)+/g, '<br />'); 
                                                      r.title = newLineToBR(htmlEncode(r.title));
                                                      r.toolTipContent = newLineToBR(htmlEncode(r.toolTipContent));
                                                  }
                                                  console.log(result);
                                                  callback(result);
                                              }
                                              else
                                              {
                                                  alert('ERROR:\n' + event.message + '\n' + event.where);
                                              }
                                              $('.loader').toggle();
                                          });                                     
                                  }                                 
                              });                        
                      });
    </script>
    
    <style>
        .loader{display:none; position:fixed; top:50%; left:50%; border: 16px solid #f3f3f3; border-top: 16px solid #3498db; border-radius: 50%; width: 120px; height: 120px; animation: spin 2s linear infinite;}
        @keyframes spin {0% { transform: rotate(0deg); }
        100% { transform: rotate(360deg); }
        }
        
         <!--Scheduled event classes-->
        .workOrder-scheduled{background:red ;border-color:red; color: white !important;}
        <!--.workOrder-scheduled td{background:red ;border-color:red; color: white !important;}-->
        .psWork-scheduled-liveDay{background:green ;border-color:green;}
        .psWork-scheduled-liveDay .fc-list-item-title{color: white !important;}
        .psWork-scheduled-installDay{background:yellow ;border-color:yellow;}
        .psWork-scheduled-regDay{background:violet ;border-color:violet;}
        .psWork-scheduled-remoteInstall{background:teal ;border-color:teal;}
        .psWork-scheduled-remoteInstall .fc-list-item-title{color: white !important;}
        .psWork-scheduled-iDStoreFlip{background:sienna ;border-color:sienna;}
        .psWork-scheduled-training{background:SpringGreen ;border-color:SpringGreen;}
        .placeholder-scheduled-holidayHalf{background:skyBlue; border-color:SkyBlue; color: black !important;}
        .placeholder-scheduled-holidayFull{background:blue; border-color:blue;}
        .placeholder-scheduled-holidayFull .fc-list-item-title{color: white !important;}
        .placeholder-scheduled-bankHoliday{background:DarkBlue; border-color:DarkBlue; }
        .placeholder-scheduled-bankHoliday .fc-list-item-title{color: white !important;}
        .placeholder-scheduled-sickness{background:green; border-color:green; color: white !important;}
        .placeholder-scheduled-sickness .fc-list-item-title{color: white !important;}
        .placeholder-scheduled-fs{background:red; border-color:red;}
        .placeholder-scheduled-fs .fc-list-item-title{color: white !important;}
        .placeholder-scheduled-ps{background:orchid; border-color:orchid; color: black !important;}
        .placeholder-scheduled-support{background:darkViolet; border-color:darkViolet;}
        .placeholder-scheduled-support .fc-list-item-title{color: white !important;}
        .placeholder-scheduled-training{background:orangeRed; border-color:orangeRed; color: black !important;}
        .placeholder-scheduled-unavailableAM{background:khaki; border-color:khaki; color: black !important;}
        .placeholder-scheduled-unavailablePM{background:khaki; border-color:khaki; color: black !important;}
        .placeholder-scheduled-office{background:DarkSeaGreen; border-color:DarkSeaGreen; color: black !important;}
        .placeholder-scheduled-garage{background:DarkSlateGray; border-color:DarkSlateGray;}
        .placeholder-scheduled-garage .fc-list-item-title{color: white !important;}
        .placeholder-scheduled-shadowFS{background:DarkRed; border-color:DarkRed;}
        .placeholder-scheduled-shadowFS .fc-list-item-title{color: white !important;}
        .placeholder-scheduled-shadowPS{background:PaleVioletRed; border-color:PaleVioletRed;}
        .placeholder-scheduled-shadowPS .fc-list-item-title{color: white !important;}
        .placeholder-scheduled-reminder{background:Gray border-color:Gray; color: white !important;}
        
        <!--Tooltip classes-->
        .tooltipevent {border-radius: 25px; padding: 20px; background:#98AFC7; position:absolute;z-index:10001;}
        .WO-tooltipevent {min-width:150px; min-height:100px; width:auto;  height:auto;}
        .PH-tooltipevent {min-width:150px; min-height:20px; max-width:150px;  height:auto; }
        .PS-tooltipevent {min-width:150px; min-height:50px; width:auto;  height:auto; }
    </style>
    <div id='calendar-container'>
        <div id='calendar'></div>
    </div> 
    <div class="loader"></div>
</apex:page>