I have the same problem every login. I dont know if this helps but I have noticed when I change login style to 'Plain' the error message mentioned appeares, but I get the themed login screen, and when I choose themed style, it gives the error message but loads Gnome Desktop Manager.
-- GDM: Greeter application crashing https://launchpad.net/bugs/48936 -- desktop-bugs mailing list desktop-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/desktop-bugs