arjuna only listens resource adapters calls through spi interface methods, i think with high probability there is a problem at your ra conf or usage at mdb. You can try to catch exceptions print stacktrace see the cause of problem. For now all i can say is its "timed out". The cause can be connection configurations or something taking more time than expiration timeout threshold.
Be sure that connection is working if this not the problem show your related mdb code so someone can help.