What was the older version of Debian using to log in, and can you go back to that?
I don't use remote login, but when I upgraded to Wheezy I found some of the features I do use in gdm2 were not working in gdm3, despite still being listed in the documentation.
In the end I uninstalled gdm3 and replaced it with gdm2 from the Sqeeze repo, which turned out to be a very easy fix: the package for gdm3 is called gdm3 (not gdm
[version 3] ), so Synaptic / Apt treats it as a different package and doesn't try to 'upgrade' from gdm [version 2].