Bug#339888: Not a bug

[Liam M. Healy]

I had this same problem, which manifested itself as a box that
appeared in front of the login screen that said 
"The configuration file contains an invalid command for the login
dialogue, so running the default command.  Please fix your
configuration."

Apparently, the maintainers changed the location of certain files.
This change was (correctly) reflected in the distributed
/etc/gdm/gdm.conf.  However, I had changed gdm.conf and when the
upgrade was installed it kept my gdm.conf and put the new one into
gdm.conf.dpkg-dist, presumably because I asked it to keep my file (the
default).  So it is necessary to manually merge the changes made in
the local configuration and the new version of gdm.  This is the
correct behavior and is not a bug.

As a side point, and this probably should be a new wishlist bug
report, I think the message about the configuration file is poorly
phrased.  It took me quite a while to figure out _what_ configuration
file contained an invalid command.  The simple addition of a file name
"The configuration file /etc/gdm/gdm.conf contains..." would have
saved time. 

Liam