Jini requires a server to deliver class files to a client. Usually this is done using an HTTP server. One of the common errors related to this is

java.rmi.ServerException: RemoteException in server thread; nested exception is:
        java.rmi.UnmarshalException: unmarshalling method/arguments; nested exception is:
        java.lang.ClassNotFoundException: could not obtain preferred value for: ...

The most likely cause of this exception is that you aren't running an HTTP server on the machine that java.rmi.server.codebase is pointing to. Note that using localhost is a common error, since it may refer to a different machine from the one intended.