Additional Domain Controller

have a Domain Contoller(PDC) which is hosting Directory
Services in Win2k Server. Now I want to setup another Domain
Controller if my primery domain gets any problem in case the
second domain should be take charge. Means I want crete Backup
Domain Controller(BDC) or Active Directory Replication shoul be
happened.

I had tried to setup Addtional Domain Controller but I
am getting Following Error in this operation.

The Directory Service failed to construct a mutual authentication
Service Principal Name (SPN) for server “Server Name”. The call
is denied. The error was:
A Service Principal Name (SPN) could not be constructed because
the provided hostname is not in the necessary format.

Please advise…..