Comment 103 for bug 349519

The fix that was mentioned before helped me.

1) Press Ctrl+Alt+F1 - that will bring up console
2) enter your login and password
3) enter this command (that's one big line, no line breaks): gconftool-2 --set /desktop/gnome/session/required_components_list --type list --list-type=string ["windowmanager","panel","filemanager"]
4) reboot your computer (by entering "sudo reboot")