help: Windows MessageBox prevents custom dialog from showing?

[heman154]

I have a gui application that is launched via createprocess(...) from another gui application (that subsequently kills itself). This new application creates a secondary thread that creates a dialog (hidden) at thread creation. I am looking for windows shutdown requests on this secondary dialog (using onQueryEndSession()), and then attempt to show this dialog. It works correctly for most cases (e.g. when I press ctrl+alt+delete and then select shutdown), but sometimes I get a "System Settings Change" Message Box which appears after new devices installed. In this scenario, my application catches and prevents the shutdown request, but fails to throw up the dialog when I use ShowWindow(SW_SHOWNORMAL) (by the way, its modeless). Does anyone know why a messagebox like this would cause this behaviour? I found that uninstalling a device brings up a similar messagebox (same caption, different text), but in this test my modeless dialog does appear. Any suggestions would be appreciated. Thanks, Himanshu