Comment 42 for bug 851055

I have a slightly different scenario here: I created a new user from the command line as I broke my original user (and that is another problem altogether) and while having fixed most permission problems using vigr, found that I couldn't shut the machine down or mount USB drives. Following the solution from christianwolf above, I looked at /etc/lightdm/lightdm.conf and found that autologin was set to the old username. Commenting that out and rebooting has given me access to the USB drive and I'm yet to test rebooting.