Comment 5 for bug 507000

This should be fixed with a fully updated lucid, from your logs it looks like you got hit with the move to alternatives in xserver deleting your libdri.so/libglx.so but that was fixed about a week ago. You can verify the packaging problem is fixed by doing a ls /usr/lib/xorg/modules/extensions/lib{glx,dri}.so and they should exist, if not running sudo apt-get install --reinstall xserver-xorg-core will fix it. It should be safe to remove nomodeset and go back to using the ati driver now, but please reopen the bug if that is not the case.