Getting Messenger

Hi,
I've a problem sending a message to another peer. I got the peer's ID 
out of his PeerAdvertisement. Then I use this code:

endpointService = myPeerGoup.getEndpointService();
EndpointAddress ep = new EndpointAddress(destinationID,null, null);

Messenger messenger = endpointService.getMessenger(ep, null);
        if (messenger == null) throw new Exception();
[...]
messenger.sendMessage(jxtaMsg);

I never reach messenger.send(), because messenger is null. The docs tell 
me, that null means, that ep is not reachable. But I got the peers 
Advertisement and he got mine. So we see each other, but can't talk to 
each other.

Have you got any hints?

Thanks and best regards
  Volker