Public Folder Replication fails one way

[Cooty]

We have a simple two site set-up using w2k sp4 servers. One site has exchange 2k the other exchange 2003. We can replicate the Exch2003 PFs on the Exch2000 server but not the other way around.
Have worked through KB842273 and can track the Exch2000 PF replication emails fron Exch2000 to the Exch2003 server using Message Tracking Centre but the last line simply says "SMTP: Advanced Queue Failed to Deliver Message"
Maximum logging enabled but we have no NDR's or any other errors logged in either server's application logs. PF email addresses seem fine and replication works in the other direction.

 

[Cooty]

Further investigation reveals that none of the replication messages sent from the Exch2k server are accepted by exch2003. Both servers send replication messages but only the exch2k (master) server accepts them. No NDRs are generated by the exch2003 server.
If I send a test message from an internal account to both server's SERVER-IS account only exch2k sends an NDR.
If I send an external test email to the exch2003 SERVER-IS account it does log an NDR in event viewer.

Can anybody confirm that this set-up should work? It seems unlikely that this is a bug between exch2k & exch2003
Thanks