Fresh install of XP followed by a fresh install of Ubuntu 12.04 results in the following error: error: unknown filesystem. grub rescue and the machine will not boot. Prior to the 12.04 install, XP worked fine. During the 12.04 install, all partitions and free space was visible, and the install seemed to complete without issues until the error message. Although I can fix the MBR via recovery console in XP and allow the machine to boot to windows, why is GRUB/Ubuntu trashing the boot sequence?