David,

I would suggest that your MapPoint control was not placed directly on your frmMain but rather on some kind of a frame window.

If the container frame name is 'Frame1', for instance, then inside 'Property Get hWnd_Frame' use that object name 'frmMain.Frame1' in place of 'frmMain'.

If it is not your case, and there is indeed an unknown problem with frmMain complexity, then resolve it by creating such a frame (specifically designated to contain MapPoint control in it). Cut and paste MapPoint on the frame and point ''Property Get hWnd_Frame' to it as discussed above.

Hope this should help,
Sergiy