I had the exact same problem and followed the steps in Comment #16. I then re-installed the ubuntu-desktop package.
After that, my upgrade to Edgy began to proceed. Thanks for the tip, Tim -- Can't calculate the upgrade with unofficial mesa/compiz packages https://launchpad.net/bugs/58424 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
