Appointment-Cannot set Categories because ConversationID is not set

[Steve Anthony]

I have had some simple code to set a category in an appointment.
This has been working until recently.

After much debugging, I've identified the root cause - appointments/meetings that come from other people.

The code still works for appointments that I create, but fails for others.
I was recently migrated from a local Exchange (2007?) to Exchange Online - unsure if this is related or not.

Simple example of the code (which will remove a category if it exists, add it if it does not):

Sub SetCategory(inCat As String)
  Dim objAppt As Object
          
  Dim i As Integer
  Dim strCats As String
  Dim bCatFound As Boolean
   
  Set objAppt = Application.ActiveExplorer.Selection.Item(1)

  strCats = objAppt.Categories
 
  If Len(strCats) = 0 Then
    objAppt.Categories = inCat
  Else
    'Check if category is already there - if so that means we need to delete
    If InStr(1, strCats, inCat) > 0 Then
      ' may not need to handle extra commas; if so, build a function
      objAppt.Categories = Replace(strCats, inCat, "")
    Else
        objAppt.Categories = inCat & "," & strCats
    End If
   
  End If
 
  Set objAppt = Nothing

End Sub

On any assignment of "objAppt.Categories", i receive the following error for appointments that I don't create:
Run-time error '440' : Object doesn't support this property or method

If I examine objAppt as a watch variable, I see :
: ConversationID : <Object doesn't support this property or method>

Since this is a read-only field, I'm befuddled at how to work around this.

Greatly appreciate any help!

Steve

 

[Steve Anthony]

One update/correction:
The code *is* working on new appointments. But appointments/meetings created before the migration seem to be those that fail.