This is known bug. Read https://help.ubuntu.com/community/DapperUpgrades#head-0171d3953a2ea19e9b4228bcd5cde3ecfb67f7af
** Changed in: ubuntu-meta (Ubuntu) Status: Unconfirmed => Rejected -- Updating from Breezy to Drake produces error unbuntu-desktop https://launchpad.net/bugs/51132 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs