If you find your system isn’t booting sometimes and you get this funny error message, edit your kernel boot line in /boot/grub/menu.lst:
kernel /boot/vmlinuz-2.6.24-19-generic root=UUID=75a92494-bdae-4715-92d9-f06d1887008e ro all_generic_ide
e.g – Add the all_generic_ide parameter. All should be fine once again. I believe this is a strange Ubuntu kernel bug, although I’m not sure.