I've just worked this problem through with a friend, and he was having the same issue.
Adding the following entry to xorg.conf under screen fixed the problem.
Option "AddARGBGLXVisuals" "True"
Tested after a reboot and everything worked fine.
I.e. ----- Section "Screen" Identifier "Default Screen" Device "NVIDIA Corporation NVIDIA Default Card" Option "AddARGBGLXVisuals" "True"
Section "Extensions" Option "Composite" "Enable" EndSection -----
I've just worked this problem through with a friend, and he was having the same issue.
Adding the following entry to xorg.conf under screen fixed the problem.
Option "AddARGBGLXVisuals" "True"
Tested after a reboot and everything worked fine.
I.e.
-----
Section "Screen"
Identifier "Default Screen"
Device "NVIDIA Corporation NVIDIA Default Card"
Option "AddARGBGLXVisuals" "True"
Section "Extensions"
Option "Composite" "Enable"
EndSection
-----