Comment 13 for bug 477832

I've had the same problem when upgrading from 9.10 (clean install) to 10.04 using the upgrade tool.

Tried to fix it by doing a sudo users-admin and fixing the permissions.
This did work at first, but after a few reboots (and maybe some updates) things started to break down again. Could not shut-down the computer, could not mount external drives (ntfs/fat). However the permissions in users-admin looked ok.