Global Catalog problem???

I have a single Windows 2K DC,( it has AD and is a GC server)and am trying to rename the built in Administrator account. The message I get is “windows cannot validate the uniqueness of this proposed user name with a global catalog server because: The search filter cannot be recognized.” The message goes on to say that it will rename the account, which it does, but the user will be unable to log on until the new name is verified. Indeed, I am unable to log on as this new user name, only as the original administrator…even though in the active directory, the account appears to be renamed. This is the only DC on the LAN, and the only DC for this domain.
Any ideas on what could be causing this behavior????