This is one of those problems that can leave you banging your head against the wall. Say you have a multiple domain forest and have Exchange 2003 installed in the parent domain. Then, say you want to give Exchange mailboxes to users in one of the child domains. Shoudl be as easy as running setup /domainprep in the child domain and then creating the new RUS through ESM?
There's an error that plagues every Exchange admin who tries this task. You go through the steps creating the RUS, choosing the Exchange Server you want to host the RUS and the domain controller in the child domain. You have everything selected, click Finish, and then, after what seems like an unusually long pause (the kind that lets you know it's not going to work), you get this message:
The RPC server is unavailable.
ID no: c00706ba
RPC errors. Great. You check firewalls on both sides--wide open. You ping the target DC's FQDN, which resolves. Retry the procedure, but it's really about as effective as slamming your hand in a car door repeatedly.
The solution is ridiculously simple, and makes sense in Exchange 2003 world. Exchange 2003 still has a lot of dependencies on NetBIOS name resolution. There are several alternatives:
1. Add a static WINS entry for the domain controller in the child domain.
2. Configure WINS replication between child and parent domains.
3. Add the hostname (not FQDN) to the hosts file in %windir%\system32\drivers\etc\hosts on the Exchange Server where you are trying to add the RUS.
4. On the network adapter properties of your Exchange server, add DNS and WINS servers for the child domain.
The problem is that the RUS wizard is looking for the NetBIOS name of the DC that's going to be used in the child domain. Unless you're replicating WINS between parent and child or pointing to a remote WINS/DNS server that has the target domain controller that you've specified for the RUS, you won't be able to resolve the short name of a domain controller in the child domain. Yes, it sucks. Even though the Exchange server is looking for a NetBIOS name, putting the short name of the DC the hosts file works due to the name resolution lookup process. If you had put the FQDN of the target DC in the hosts file, you'd still have the problem--remember, you can already ping the FQDN, so putting it in a local hosts file isn't going to fix your problem.
The real tricky part of figuring this out is that during the RUS creation process, the wizard tells you the FQDN of the target domain controller in the child domain, yet it attempts to contact only the NetBIOS name of the DC.
You may also want to check to make sure that the Exchange Domain Servers and Exchange Enterprise servers groups have been created (should have been done through the Exchange setup /domainprep command) and are in the default Users container.