I wonder if anyone else is having this problem. The grub2 installed with Natty is hit and miss on seeing and mounting other partitions and drives. I run 10.10 on sda1 and natty on sdb1.
I let Natty reinstall grub2 and half of the time neither operating system would see or mount drives set up in fstab. By reinstalling grub2 from the 10.10 live CD and updating grub both systems now boot normally and recognize all partitions.