>Does it "lock-up" when a messagebox, instead of a MODAL, is called from the MDI child form.
>
>Try to give focus to some object on the MDI child (like a button or text box) with a setfocus() before the MDI child calls the MODAL form. Maybe the init state is not complete when the MODAL is called.

Regardless VFP must give a VFP's internal error message even it's about my mistake, but in that case VFP crashes.

modal and maximized amd MDI are needed for that bug.