RAID 1 and grub

I have a machine with Fedora core 8 installed onto RAID1 on IDE drives - 
hda and hdc.

hda has failed and after spending some time with a rescue disk mounting 
hdc's /boot partition (hdc1) and changing the grub.conf device 
parameters, I have no success in booting off it.

I then set them back to the original (hd0,0) and moved hdc into hda's 
position.

Booting from there brings up the message: GRUB hard disk error

Can any grub guru offer any assisentence as to what may be missing here?

Regards,

Richard