Active Directory will not replicate.

I an trying to setup an exchange 2000 server, I believe I am having trouble seting it up because the Active Directory is not replicating to the machine. I have entered AD Sites and Services and opened up the exchange server, setup a connection and Ireceive the following error when I try to replicate now “The DSA operation is unable to proceed because od a DNS failure” or when I left click NTDS Settings | Check replication topology I get the error AD property cannot be found in cache. I have double checked DNS all seems OK. Please Help!