Open Form Error when Form is Open?

[ActMod]

Periodically (but not always), I get an error message suggesting that a Form which contains a ListBox is not "Open" when I attempt to access the ListBox. Can someone suggest a test that will ensure that Access is treating the Form as Open - and, if not, will open the form. I use the following statement to open the Form:

DoCmd.OpenForm "frmForm1", acNormal

I have put a breakpoint between the "open Form" statement and my attempt to access the ListBox to ensure that frmForm1 is, in fact, open prior to accessing the ListBox. Even when frmForm1 is open, for some reason Access occassionally treats it as closed and gives me an error message.

Any help with this ongoing frustration would be greatly appreciated.

Jim