The company that I was recently working for was in the middle of a global Windows 2000 migration project throughout which we encountered many interesting problems. In most of our offices, we kept encountering a remote procedure call (RPC) server error. Because we were in the middle of a Win2K migration, all user accounts were in the new Win2K domain, while all the resource servers were still in the old Windows NT 4.0 domain. When we attempted to add a user from the Win2K domain to a Microsoft Exchange Server or IIS system (e.g., make the user the primary owner of a mailbox on the Exchange Server or IIS system), the server kept returning the following error message: Unable to browse the selected domain because the following error occurred: The RPC server is unavailable.

Immediately, we suspected that the problem was communication between the NT Server system and the Win2K domain controller (DC). To work around this problem, we used User Manager (you could also use Server Manager—both tools communicate with the Win2K DC holding the PDC Emulator master operations role), which worked perfectly. Because our Win2K DC was also a WINS server, we changed the WINS settings on the affected Exchange Server system to use the WINS server running on the PDC Emulator. This workaround immediately fixed the problem. We then completed this change on all the affected servers. This solution highlights how important a role the PDC Emulator plays in a mixed Win2K and NT 4.0 environment.