The original error (failed to load OS), i got with GRUB 2, and GRUB 1 under special circumstances. My haiku partition is (hd0,4) on grub 1 and (hd1,4) on grub 2. These caused it to fail to boot: grub2: set root=(hd1,4) chainloader +1 boot chainloader (hd1,4)+1 boot grub1: chainloader (hd0,4)+1 boot THIS is the only solution that worked, and only with GRUB 1. I filed a ticket about it. root (hd0,4) chainloader +1 boot --- For some reason, having root read the drive and then chainloading worked. I had turned on the stage1 debug messages, and it only said 'read error' before.