[Bug 33783] Login using XDCMP gives blank window

[LCID Fire]

Public bug reported:
https://launchpad.net/malone/bugs/33783

Affects: gdm (Ubuntu)
       Severity: Normal
       Priority: (none set)
         Status: Unconfirmed

Description:
When I try to login from a Breezy machine to a Dapper one (via XDCMP) after entering the login info I just get a blank screen and nothing more. This already worked in dapper - but broke a few month ago.
AFAIC there is no error message written. Also - I already tried deleting the .gnome2 and .gconf folders - to no avail.