Clebert,
thank you very much for your help. Renaming the queues as you suggested and fixing a "small" bug (starting the client session on the receiving node at the right time!) have let me succeed in sending a message from one client to the other.
Frank Sherwood
Just a tip: Don't forget to ACK your messages on the client side. (I didn't see that in any of your examples).
(or you could also use pre-ack, but that would be dependent in your requirements and how would you like to reply message sends in case of a network failure).