When you use the Windows 2000 Support Tools, from the Server CD-ROM, on your Windows 2000 Professional workstation, to create a user in the Active Directory, you receive:
Windows cannot validate the uniqueness of the proposed user name with global catalog server because:
The server is not operational. Windows will create this user account, but the user can log on only after the user name is verified to be unique. For further assistance, contact your system administrator"
Your workstation can not find the Global Catalog server, which it needs to check the uniqueness of the UPN.
By default, the GC is the first DC in the forest.
This is likely to be a DNS issue. To resolve the problem, stop and restart the Netlogon service on the GC to force registration of the GC in DNS.
NOTE: The following tips may be germain to this issue: