Ubuntu 11.04 Unity / Classic load fails - remains at background without toolbars / windows
Solution 1:
Change the GRUB_CMDLINE_LINUX_DEFAULT in /etc/default/grub in:
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash radeon.modeset=1 pci=nomsi"
Run update-grub and reboot
The pci=nomsi did the trick for me.