In the Remoting detection facility, there are two kinds of detectors: client detectors and server detectors. Note that these should not be confused with client invokers and server invokers.
A server detector is responsible for publishing the existence of all server invokers running in the same JVM. A client detector will, in addition, keep track of all server invokers that it has detected, and when it notices the appearance of a new server invoker or the disappearance of a known server invoker, it will notify all registered listeners of the change in the network.
Notifying listeners of network changes is performed by an org.jboss.remoting.network.NetworkRegistry. A detector queries its MBeanServer to retrieve a NetworkRegistry, but if none is available, it is unable to make notifications. In other words, if a detector cannot locate a NetworkRegistry, it is, by definition, a server detector. The message
Detector: org.jboss.remoting.detection.multicast.MulticastDetector could not be loaded because the NetworkRegistry is not registered
This means that only the broadcasting of detection messages will be functional and will not be able to discover other servers.
means that you did not register a NetworkRegistry with the MBeanServer and listeners will not be informed of the discovery of new servers (or the disappearance of old ones).
For an example of how to set up detection, see the classes org.jboss.remoting.samples.detection.multicast.SimpleDetectorClient and org.jboss.remoting.samples.detection.multicast.SimpleDetectorServer in the Remoting source code tree.