remounting a drive

[Steel City Phantom]

ok, i had a working bsd system.

i shut it down, and removed a drive from it to use in another computer

i turn it on and i get mounting errors, nothing unsual, can't find drives

from the manualroot prompt i put in the path to the root partition to 
the drive that is still in the machine

i boot to single user mode

im now trying to edit my fstab so i can boot normally (the drive numbers 
moved from ad1 to ad0 because i removed a hardrive)

i can see all the files, i mounted my /usr partition, but for some 
reason i can't remount the / parition to edit the fstab.  when i enter 
the command mount -o rw / i get operation not permitted.  i tried mount 
-o rw /dev/ad1s1 /  and mount -o rw /dev/ad0s1 /and got the same thing.  
ive used this in the past and it works, i don't know why its not working 
now.  any ideas?

bsd 6.2 if it matters

when i do mount
/dev/ad1s1 on / (ufs, local, read-only)
devfs on /dev (devfs, local)
/dev/ad1s1f on /usr/ (ufs, local, soft-updates)

thanks
willie