Linux: X server crashes

Long time ago, I have a problem that my X server crashed when I change my current profile from one network profile in net applet. I had no clue at all then. I remember that I changed .gnome and some directories, then the problem is gone. But I have to use kde then. Today I logon gnome and X server crashed again. I cannot fix it by upgrading using installation disk. And I create a new account, it is working well. And I searched the internet and realized that some people also have the same problem with me. Actually the problem is from 3D effect. I have to edit the file: /etc/X11/xorg.conf to comment two lines which is bad for x server. They are:

Option "Composite"
Option "XaaNoOffscreenPixmaps" "1"

After removal, I can restart X server. :-)