Comment 4 for bug 115609

Please install the xserver-xorg-core-dbg package, it can help make the backtrace in the server log more complete. If you could do more debugging it would be great, see https://wiki.ubuntu.com/DebuggingXorg for some tips. Please try the newest drivers from https://wiki.ubuntu.com/XorgOnTheEdge also. I have seen this on an ati card before, but not with the newest drivers.