gdm fails to start X with autologin

Binary package hint: gdm

Problem:
Network upgrade from Intrepid to Jaunty with Xubuntu. On reboot after upgrade, normal bootup, but error message:

'No exec in session file: .xfce4' (Can't remember the exact words - this is close).

Then gdm defaults to a failsafe X mode with just an xterm. Rebooting, playing around & looking in logs revealed nothing and fixed nothing.

Fix:
Typed 'exit' at xterm (I see you've disabled alt-ctrl-bksp) to get back to GDM. Logged in and got message:

'No default session manager. Do you want to make xfce your default?'

That seems to have fixed the problem for good.

Hardware:
Acer Aspire One
Standard Xubuntu (not lpia)