computer name has already been added to a Windows 2000 domain. For more details, please refer to the troubleshooting section in the DSMN documentation.
If you add a NetWare server to the DSMN in a Windows 2000 domain and later abandon the domain, you will be barred from adding that NetWare server to a different Windows 2000 domain. When Windows 2000 tries to add a NetWare server to its domain, it looks to see if the account Winnt_Synch_Agent is already on the NetWare server. If that account is present, you will receive the following error message: <servername> has already been added to a Windows 2000 Domain.
To solve this problem, either release the NetWare server in DSMN from the original domain or delete the Winnt_Synch_Agent account on the NetWare server. If you delete the account, you may need to restore the bindery before you'll be able to add the NetWare server to the new Windows 2000 domain.