' das kommt alles in ein klassenmodul und CallProc wird aufgerufen
Private Declare Sub CopyMemory Lib "kernel32.dll" Alias "RtlMoveMemory" (ByRef _
  Destination As Any, ByRef Source As Any, ByVal Length As Long)
Private Declare Function CallWindowProc Lib "user32.dll" Alias _
"CallWindowProcA" (ByVal lpPrevWndFunc As Long, ByVal hwnd As Long, ByVal msg _
As Long, ByVal wparam As Long, ByVal lparam As Long) As Long
 
Public Function TestProc(ByVal hwnd As Long, ByVal umsg As Long, ByVal wparam _
  As Long, ByVal lparam As Long) As Long
  MsgBox "juhu!"
End Function
 
Public Sub CallProc()
  Dim addr As Long
  CopyMemory addr, ByVal ObjPtr(Me), 4
  CopyMemory addr, ByVal addr + 28, 4
  CallWindowProc addr, 12, 34, 56, 78 ' <- hier tritt der fehler auf
End Sub