Comment 5 for bug 753014

Hmm, ok this particular one looks like a "no symptom" gpu lockup, which is basically a dupe to 752940 and 767475 and similar bugs. It is caused by a conflict with the vesafb kernel module. You can use the xdiagnose utility to disable that module (or do it manually by blacklisting and/or modifying grub if you prefer the technical route), which should suppress that error.

You may also be experiencing a real gpu lockup as a separate bug. There is a commonly experienced lockup bug in natty which is particular to i945, for which I have a fix in my PPA:

https://launchpad.net/~bryce/+archive/fig

My hypothesis is that between disabling vesafb and installing this PPA, your gpu lockup error popups and freezes should either go away entirely or be much, much less frequent. Please let me know what you find, so we can proceed with a permanent fix.