I think what you are seeing is a network problem between your client and server that is preventing the acknowledgement going through. Looking at the code SessionAspect::handlePostDeliver: | if (cancel) | { | sd.cancelDeliveries(acks); | } | else | { | sd.acknowledge(ack); | } | state.getToAck().clear(); | The unacked message state is not cleared if the acknowledge throws an exception, so this would explain why the next call to handlePostDeliver gives you an IllegalStateException. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4017560#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...