Comment 84 for bug 1041883

Hmm, same problem here with Quantal. As described, system won't boot unless the procedure is made through the recovery option in the grub. This way Ubuntu loads but brightness of the screen can not be changed because "/sys/class/backglight/..." thing is not up.

Somehow, after upgrade, it once booted up normally with no error (kernel panic) and fully functional. Nevertheless, the next boot was again the same with a kernel panic :'(