After a grub update, we were instrusted to do install the new version's stage1 to MBR. A first attempt failed as follow:

# grub-install hd0
/dev/sda1 does not have any corresponding BIOS drive.

(hd0 was the boot disk for this system. You can find out yours from your grub.conf file.) To fix this problem, we just needed to add the "--recheck" option:

# grub-install --recheck hd0
Probing devices to guess BIOS drives. This may take a long time.
Installation finished. No error reported.
This is the contents of the device map /boot/grub/device.map.
Check if this is correct or not. If any of the lines is incorrect,
fix it and re-run the script `grub-install'.

And that took care of it.