Comment 58 for bug 459639

I think Alexia may be right. I'm having the same trouble with gdm. There are several bug reports scattered around that look like the same issue. Some of them do not involve nvidia, but have the same symptoms.

How could one script a check to make sure /some/ graphics driver is loaded before starting the login manager? That would be more elegant and efficient than a sleep, and more effective than just checking for nvidia.

similar bug reports:
532436 - failure possibly related to nvidia
573455 - i marked this as a duplicate of 532436
581302 - the description contains different details and is not connected to the nvidia driver, but the login manager fails in the same manner.
498315 - similar problem as I am having now, but I haven't looked into this yet. I also use ureadahead and this report proposes a connection
587607 - probably a duplicate of 581302, but not yet expired
496796 - probably unrelated, but worth a look
447226 - probably unrelated, but worth a look
forum thread (probably not the only one):
http://ubuntuforums.org/showthread.php?p=9742515