Comment 2 for bug 613150

error there is:

Removing gdm ...
Please be sure to run "dpkg-reconfigure kdm".
Purging configuration files for gdm ...
Removing user `gdm' ...
Warning: group `gdm' has no more members.
userdel: user gdm is currently logged in
/usr/sbin/deluser: `/usr/sbin/userdel gdm' returned error code 8. Exiting.
dpkg: error processing gdm (--purge):
 subprocess installed post-removal script returned error exit status 1
Processing triggers for ureadahead ...