I would hate to see what happens when you cause a "complicated" error.

Can you define what you mean when you say you are calling a form from within a datagrid? What even triggers this? Modal?

Can you isolate the problem? if you put a button on a form and try and call that same "problem" form, does it bomb?

How are you hooking up the data in the first and second grids?
data controls? manually? combination of both?

Are they reading/locking/editing the same records?