Check with JNDIView how the RMIAdaptor is registered in the server's JNDI. It has the pattern of "jmx::rmi". It could be that it has registered itself with a fully qualified domain name or something else. Also make sure the client that is trying to access the MBean has jndi.properties set correctly to point to the JNDI of the running JBoss server.
I get a classcastexception thrown in the RMIClientConnectorImpl. Any ideas as to why it might do that?