I have a lenny system with Gnome and gdm. Things work pretty well, but when I try to log out and log in again the computer freezes and I have to restart.

I can log in fine (when I start the computer), and I can shutdown from gnome normally, but when I try to log out (like when I change my x configuration and I want to restart the xserver, or if I change what groups I'm a part of and I want to log in again) the computer freezes. First most of the items on the screen disappear, as if it was about to log out normally, but all activity stops. The screen is usually the same shade as the normal gnome background color (it never gets to the point where it turns black). I cannot kill the xsession either. Ctrl-Alt-Backspace doesn't work. I'm thinking it's either a gdm problem or a X problem. Has anyone else experienced this?

Any help would be appreciated. TIA.

Well, I figured it out for myself. It seems a few months ago I tried to install compiz and I read someplace that you had to edit your xorg.conf file so that it contained the line 'Load ddc' in the modules section. Well, compiz failed on my machine, and I uninstalled it, but I forgot to remove the line 'Load ddc'. Removing it now solved my logout problem. Does anybody know what ddc does? I've googled a little but found nothing. TIA .

You googled very little I take it . First hit is: http://en.wikipedia.org/wiki/Display_Data_Channel
ddc probes the monitor for sync rates and resolutions. Not really needed if you already have them set up in xorg.conf.