strange cd key error on lan

[Higgs]

A buddy and I are at his house and when we try to connect to the same server we get a cd key is invalid but when we connect to separate servers we can join no problem.

The thing is we both have two separate cd keys and two separate accounts and we just spent more than an hour to find a fix but nothing on it we both tried the reg edit fix and still can't play on the same server.

any answers?