This is a common bug with the Livna series of nvidia video card drivers.
Make sure the following 3 lines are in your xorg.conf in the "files" section:

Section "Files"
         ModulePath "/usr/lib/xorg/modules/extensions/nvidia"
         ModulePath "/usr/lib/xorg/modules/extensions"
         ModulePath "/usr/lib/xorg/modules"
EndSection