Same problem here on my machine (msi p965 neo, core 2 duo), adept upgrader reports the same problem and an sudo apt-get upgrade doesnt work too.
Not upgrading x11-common reports the same error, i had to take out xorg and xserver-xorg too, then it works. -- debconf error on upgrade install [feisty] https://launchpad.net/bugs/85800 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs