John:

The as a top level form is used when you have a form that will be like a VFP main screen. Also is used when you have a system that will use a Menu where all other form called from the menu will be defined as in top level form.

If you have a system that no going to work under Menus, and you prefer have visual foxpro main screen in the background use a definition of 0 or In Screen (Default) . That way your preview screen will be show and this problem of freezzing disapear.

But if you want have your own Main Screen in the back, define your first screen o main form as a top level form and all other form as a in a top level form. Another point that have to know is that a top level form always is modaless so you need to put read event in the activate event and clear events in the unload of the form that going to be your main form.