Comment 1 for bug 67843

I updated the system executing:
gksu "update-manager -c -d"

But the upgrade failed because there were an unknown file on /usr/X11R6/bin: the installer didn't give me a chance to remove or move the file, just abort the upgrade.

I deleted the offending file and rerun the installer with the same command, but it reported broken packages and refused to run.

So I ran an "sudo apt-get dist-upgrade -f" to continue the upgrade process.

Then I rerun gksu "update-manager -c -d", and rebooted. The X server didn't run an a text dialog appeared on the screen saying that there were an ABI mismatch between the radeon driver and the xorg core.

I ran "sudo apt-get install xserver-xorg-video-ati" and the problem was solved.