Another thing to try is disabling Composite Extensions by adding:
Code:
Section "Extensions"
Option "Composite" "Disable"
EndSection
to your xorg.conf file. I don't know if this will help or not, but I got the same exact error running K/Ubuntu Edgy(6.10) and Fiesty(7.04). I found out that Composite extensions were enabled by default starting with K/Ubuntu version Edgy (6.10) and later.