Comment 10 for bug 785762

On a side note, update manager suggested removing ugr-desktop-g3 and reinstalling ubuntu-desktop as a solution in my case. apt-get and aptitude tried to fix it with no avail. The steps above work.

Issues like this sometimes happen with the GNOME 3 team's packages, as they might update package versions at different times. If they don't update ones that depend on each other at the same time, they might have clashes. I hope that they will work this out.