As you release each form, the Forms() array gets re-dimensioned and the forms get renumbered from 1 to FormCount. Therefore, at some point you will be attempting to access a form object that is outside of the Forms array.

Try something like this:

FOR EACH lo_Form IN _SCREEN.Forms
   IF .NOT. UPPER(lo_Form.Name) == "FRMMAIN"
      lo_Form.Release()
   ENDIF
ENDFOR

>I'm trying to release all forms, other than the main form, when a button is clicked. They are not in a form set. The code works fine when the main form and one other form are open, but once I open more forms the code fails with a "FORMS is not an object error."
>
>For i=1 to _screen.formcount
> If _screen.forms(i).name<>"frmMain"
> _Screen.forms(i).release
> Endif
>Endfor