switching from kde to gnome

[Marco]

Hello,

I installed ubuntu and quite soon I installed the kubuntu desktop and worked
with kde. Now I want to switch to gnome.

I can start a gnome session from the kdm login screen without a problem. But
if I set gdm as default display manager I can't start neither gnome nor
kde. The start of the session abort immediatly and .xsession-errors shows:

/etc/gdm/PreSession/Default: Registering your session with wtmp and utmp
/etc/gdm/PreSession/Default:
running: /usr/bin/sessreg -a -w /var/log/wtmp -u /var/run/utmp -x "/var/lib/gdm/:0.Xservers" -h "" -l ":0" "user"
/etc/gdm/Xsession: Beginning session setup...
/etc/bash_completion.d/apt-file: line 37: `_apt-file': not a valid
identifier

Any suggestions are appreciated.

Regards,
Marco