Try this:
Private Sub MPC_BeforeClick(ByVal Button As Long, ByVal Shift As Long,
ByVal X As Long, ByVal Y As Long, Cancel As Boolean)

On Error Resume Next
Set oResults = MPC.ActiveMap.ObjectsFromPoint(X, Y)
For Each oResult In oResults
If TypeOf oResult Is Pushpin Then
Cancel = True

...........
You only use "Cancel=True" if it is a Pushpin what you have selected