Dan,
2 things...
First, have you verified that oAppForm is being set the way you believe it should be set? (maybe you already mentioned that you checked that)
If not, then I agree with Einar, you may want to step through the show() to see what's going on.
This might be a stretch, but have you very recently added anything to the form class that your 'oForm' uses, and that might be causing the problem?
Kevin