http://linux-knowledgebase.com/en/Tipoftheday/February/error23errorwhileparsingnumber
saved my server. It wasn’t booting after an upgrade to Debian Squeeze, despite following the upgrade instructions. Connecting to the serial console showed there were problems with finding root (grub error while parsing number, error 23) which was at md1.

Changing the first line to root (hd0,0) and adding initrd /boot/initrd.img-2.6.32-5-amd64 allowed the system to boot normally. I’m not sure why grub-setup didn’t add the initrd line, but I can forgive that as it’s working now.

Remember to update grub’s config once you have it booting.