Does this happen only when you have compiz (aka Visual Effects) turned on? This sounds similar to a bug we saw reported a lot for 945 where X would crash because the i945 is limited to a 2048x2048 texture buffer.
Also, if possible it would be helpful if you could test this against natty, in case the issue is already fixed.
Please collect a full backtrace - see http:// wiki.ubuntu. com/X/Backtraci ng for directions.
Does this happen only when you have compiz (aka Visual Effects) turned on? This sounds similar to a bug we saw reported a lot for 945 where X would crash because the i945 is limited to a 2048x2048 texture buffer.
Also, if possible it would be helpful if you could test this against natty, in case the issue is already fixed.