What limitations exist for using API calls via VBA versus VB6?

I'm trying to get the handle to an ActiveX control on an Access 2000 form via:

Code:
      Private Declare Function FindWindowEx Lib "user32" _
         Alias "FindWindowExA" _
         (ByVal hWnd1 As Long, _
         ByVal hWnd2 As Long, _
         ByVal lpsz1 As String, _
         ByVal lpsz2 As String) As Long

      Private calendarHwnd As Long
in form load:
Code:
calendarHwnd = FindWindowEx(Me.hwnd, 0&, "CalendarWndClass", _
            vbNullString)
In Access VBA calendarHwnd is always evaluated as 0, which means unsuccessful. On a VB6 form it works fine.

Code was taken was MS KnowledgeBase because to resolve the fact that the Calendar Control has Comboboxes with the Month and the Year that have change events, but the control doesn't keep track of what they changed to.

Thanks,
Josh
VS6 SP4