It happened to me also when I upgraded from 12.04 --> 14.04 --> 14.10. It occurred after the second update (to 14.10). The solution from comment #9 fixed it.
It happened to me also when I upgraded from 12.04 --> 14.04 --> 14.10. It occurred after the second update (to 14.10). The solution from comment #9 fixed it.