Moving SBS 2000 domain to new 2003 R2 Server

We recently bought a new and more powerful server in order to run Microsoft Great-Plains accounting software. The new server is running Server 2003 R2 Standard Edition 32bit and was simply added to our current SBS 2000 domain as a second DC. We have since transferred any necessary apps to the new server having done away with Exchange Server in favour of mDaemon. I now want to decomission the old SBS 2000 server and transfer all domain management and server roles to the new 2003 server but running DCPROMO on the old server fails, saying that it 'Failed finding a suitable domain controller for the domain xxxx.co.uk'  and that the 'specified domain either does not ecist or could not be contacted'. DNS is working fine on both machines, and I've pointed the SBS 2000 DNS to each server in turn to try and alleviate the problem, but still I cannot demote the SBS server. BTW I have also flagged the new server as GC and removed it from the old server.