Comment 6 for bug 367334

I saw similar phenomena with my system.
After logout from KDE, the screen is blacked out, and could not see gdm login screen, and could not login from virtual console neither.
The system was able to respond to ping from another machine.
It seems that re-creation of the phenomena is easier with linux-image-2.6.28-3-rt than with linux-image-2.6.28-15-generic .
I'm using nvidia Quadro4, not Radeon. The output of lspci is:
01:00.0 VGA compatible controller: nVidia Corporation NV17GL [Quadro4 550 XGL] (rev a3)
And somebody claim that he is suffering same problem with Intel Xserver in Japanese forums.
So I don't think it is caused by the Xserver.

I found some warning/error in my system's log file:

daemon.log:Oct 17 16:30:02 my-system console-kit-daemon[3150]: WARNING: Couldn't read /proc/3149/environ: Failed to open file '/proc/3149/environ': No such file or directory

syslog:Oct 17 16:30:40 my-system gdm[4045]: CRITICAL: gdm_config_value_get_bool: assertion `value->type == GDM_CONFIG_VALUE_BOOL' failed

Please give me some ideas to find out the cause of this problem.
Regrads.