Can you try to create all the partitions through Debian's installer. I have a suspicion that partition type may be wrong for BIOS partition. You have specified ext2 as file system for BIOS grub which may mean Linux partition instead of BIOS grub partition (ef02 BIOS boot).
In the end, it was actually the lack of /boot partition that caused the problem (as Steve McIntyre explained in another message in this thread).