InvalidCallbackException when setting authenticator from MetaCallback

gistfile1.py

#!/usr/bin/env python
# -*- coding: utf-8
import Ice, sys, time
Ice.loadSlice('', ['-I' + Ice.getSliceDir(), 'Murmur.ice'])
import Murmur

class MetaCallbackI(Murmur.MetaCallback):
    def started(self, server, current=None):
      print "From MetaCallbackI : Attaching callbacks to virtual server %d." % server.id()

      print "... Attaching server callbacks"
      serverR=Murmur.ServerCallbackPrx.uncheckedCast(current.adapter.addWithUUID(ServerCallbackI()))
      server.addCallback(serverR)

      print "... Attaching authenticator callbacks"
      authR=Murmur.ServerUpdatingAuthenticatorPrx.uncheckedCast(current.adapter.addWithUUID(ServerAuthenticatorI()))
      server.setAuthenticator(authR)

    def stopped(self, server, current=None):
      pass

class ServerAuthenticatorI(Murmur.ServerUpdatingAuthenticator):
    def authenticate(self, name, pw, certlist, certhash, strong, current=None):
      groups = ("GroupA", "GroupB");
      if (name == "One"):
        if (pw == "Magic"):
          return (1, "One", groups)
        else:
          return (-1, None, None)
      return (-2, None, None)

    def getInfo(self, id, current=None):
      print "getInfo ", id
      return (False, {})

    def nameToId(self, name, current=None):
      return -2;

    def idToName(self, id, current=None):
      return None

    def idToTexture(self, id, current=None):
      print "idToTexture", id
      return None

    def registerUser(self, name, current=None):
      print "Someone tried to register ", name
      return -2

    def unregisterUser(self, id, current=None):
      print "Unregister ", id
      return -2

    def getRegistration(self, id, current=None):
      return (-2, None, None)
    
    def setInfo(self, id, info, current=None):
      print "Set", id, info
      return -1

    def setTexture(self, id, texture, current=None):
      print "Texture", id
      return -1

class ServerCallbackI(Murmur.ServerCallback):
    def userConnected(self, state, current=None):
      print"userConnected ", state.userid
      pass

    def userDisconnected(self, state, current=None):
      print"userDisconnected ", state.userid
      pass

    def userStateChanged(self, state, current=None):
      print"userStateChanged ", state.userid
      pass

    def userTextMessage(self, state, message, current=None):
      print"userTextMessage ", state.userid
      pass

    def channelCreated(self, state, current=None):
      print"channelCreated ", state.id
      pass

    def channelRemoved(self, state, current=None):
      print"channelRemoved ", state.id
      pass

    def channelStateChanged(self, state):
      print"channelStateChanged ", state.id
      pass

if __name__ == "__main__":
    print "Creating callbacks..."

    init_data = Ice.InitializationData()
    init_data.properties = Ice.createProperties([])
    init_data.properties.setProperty("Ice.ImplicitContext", "Shared")
    init_data.properties.setProperty("Ice.Default.EncodingVersion", "1.0")

    ice = Ice.initialize(init_data)
    ice.getImplicitContext().put("secret", "secret")

    meta = Murmur.MetaPrx.checkedCast(ice.stringToProxy('Meta:tcp -h 127.0.0.1 -p 6502'))

    adapter = ice.createObjectAdapterWithEndpoints("Callback.Client", "tcp -h 127.0.0.1")
    adapter.activate()

    metaR=Murmur.MetaCallbackPrx.uncheckedCast(adapter.addWithUUID(MetaCallbackI()))
    meta.addCallback(metaR)

    for server in meta.getBootedServers():
      print "Attaching callbacks to virtual server %d running Mumble" % server.id()

      serverR=Murmur.ServerCallbackPrx.uncheckedCast(adapter.addWithUUID(ServerCallbackI()))
      server.addCallback(serverR)

      authR=Murmur.ServerUpdatingAuthenticatorPrx.uncheckedCast(adapter.addWithUUID(ServerAuthenticatorI()))
      server.setAuthenticator(authR)

    try:
        ice.waitForShutdown()
    except KeyboardInterrupt:
        print "CTRL-C caught, aborting"

    meta.removeCallback(metaR)
    ice.shutdown()
    print "Goodbye"