I have replicated the root cause of MultiThreadFailoverTest in a better scenario (single-threaded). If a failure happens on the middle of an ACK invocation. (actually if it happens right after the ACK is completed, on the way back of the response), the message can't be found on the new server, as the message was already ACKed on the previous server. Maybe we should ignore failures if can't find the ACK. FailoverTest::testFailureRightAfterACK is failing because of this. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4010271#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...