Just a quick fix.
I was trying to connect a primary site to a our college’s new CAS server today and kept getting the error, “The setup login user does not have sufficient permission to configure replication with specified central administration site”. In the Event Log, I found “Kerberos EventID 4”. After some googling, it turned out to be the fact that there was a computer in my local domain with the same name as the CAS server in the remote domain. Once I renamed the server in my domain, things connected properly.
This is a case where the SCCM installer should really have a better idea of the problem assuming that’s possible.