I've just installed Debian 5.0.1 (i386; network install) and I've run into a bizarre issue that I have no idea how to troubleshoot.

If I log on as (e.g.) User1, log off, and then try to log on again as User2, X-based (i.e. not terminal) software will fail to load until I reboot. After logging on as User2, all X software (including the Gnome interface) will display its interface for a fraction of a second before vanishing from the screen and the task bar. One time the Gnome interface wouldn't load after log-on: the taskbar and menubar repeatedly flashed on and off the screen as Gnome repeatedly tried and failed to load.

It doesn't matter if I log in as User2 first and then as User1. I have the same problem as soon as I try to log in under a different identity.

Any ideas?

When you log in as the second user, open a terminal and open up an application from there such as "pidgin". Is there any useful information printed when the application crashes/closes?