DoCmd.OpenForm fails when Access not the active window

DoCmd.OpenForm fails when Access not the active window.
I have an Access 2000 application which, on startup, always launches a 'switchboard' form and sometimes gets information from the user during the startup. Both forms are opened with VBA using DoCmd.OpenForm; the switchboard opens as acNormal and the input form (when used) as acDialog.

Under normal circumstances this works fine.

If, however, the Access window ceases to be the active window in Windows (e.g. the user selects another application's window in the taskbar) the forms do not open (all other VBA code runs correctly).

Any ideas?

Simon