DataServiceQueryException

I have been struggling with a small piece of code that is in the following blog:


http://blogs.msdn.com/b/bethmassi/archive/2010/06/28/integrate-outlook-appointments-with-sharepoint-2010-calendar-lists-using-data-services.aspx

The problem is that when I run the code I get the following exception:

    System.Data.Services.Client.DataServiceQueryException was unhandled by user code
      HResult=-2146233079
      Message=An error occurred while processing this request.
      Source=Microsoft.Data.Services.Client
      StackTrace:
           at System.Data.Services.Client.DataServiceRequest.Execute[TElement](DataServiceContext context, QueryComponents queryComponents)
           at System.Data.Services.Client.DataServiceQuery`1.Execute()
           at System.Data.Services.Client.DataServiceQuery`1.GetEnumerator()
           at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
           at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
           at UpdateSharePointCalendar.ThisAddIn.GetSPCalendarData(DateTime theDate) in C:\Users\ian\documents\visual studio 2012\Projects\UpdateSharePointCalendar\UpdateSharePointCalendar\ThisAddIn.vb:line 35
           at UpdateSharePointCalendar.FormRegion1.PopulateDataGrid() in C:\Users\ian\documents\visual studio 2012\Projects\UpdateSharePointCalendar\UpdateSharePointCalendar\FormRegion1.vb:line 64
           at UpdateSharePointCalendar.FormRegion1.AddToSharePoint_FormRegionShowing(Object sender, EventArgs e) in C:\Users\ian\documents\visual studio 2012\Projects\UpdateSharePointCalendar\UpdateSharePointCalendar\FormRegion1.vb:line 60
           at System.EventHandler.Invoke(Object sender, EventArgs e)
           at Microsoft.Office.Tools.Outlook.FormRegionControlImpl.Microsoft.Office.Tools.Outlook.IFormRegion.OnStartup()
           at Microsoft.Office.Tools.Outlook.FormRegionBase.OnStartup()
           at Microsoft.Office.Tools.Outlook.FormRegionManagerImpl.Microsoft.Office.Interop.Outlook._FormRegionStartup.BeforeFormRegionShow(FormRegion outlookFormRegion)
      InnerException: System.Data.Services.Client.DataServiceClientException
           HResult=-2146233079
           Message=403 FORBIDDEN
           Source=Microsoft.Data.Services.Client
           StatusCode=403
           StackTrace:
                at System.Data.Services.Client.QueryResult.ExecuteQuery(DataServiceContext context)
                at System.Data.Services.Client.DataServiceRequest.Execute[TElement](DataServiceContext context, QueryComponents queryComponents)
           InnerException:

This happens on the follwing section of code:

Public Function GetSPCalendarData(ByVal theDate As Date) As List(Of CalendarItem)  
Dim results = From ci In SPContext.Calendar 
Where CDate(ci.StartTime) = theDate  
Return results.ToList()
End Function

Can anyone suggest a solution to this, so that the grid can be filled and the appointment be created as required.

Best regards and thanks in advance
Ian