Comment 7 for bug 438789

Same bug in my case, but with "gdm 2.28.0-0ubuntu12".

As other have mentioned, I also performed the apt-get upgrade process as root when this happened.

"dpkg -s gdm" show the status as "install ok installed", but apt.log has the following:

Setting up gdm (2.28.0-0ubuntu12) ...
Installing new version of config file /etc/init/gdm.conf ...
Error setting value: Failed to contact configuration server; some possible causes are that you need to enable TCP/IP networking for ORBit, or you have stale NFS locks due to a system crash. See http://projects.gnome.org/gconf/ for information. (Details - 1: Failed to get connection to session: Did not receive a reply. Possible causes include: the remote application did not send a reply, the message bus security policy blocked the reply, the reply timeout expired, or the network connection was broken.)
dpkg: error processing gdm (--configure):
 subprocess installed post-installation script returned error exit status 1