We get this Exception on jboss 4.0.4GA with ejb3 config and messaging 1.0.1.CR4, using ejb3 mdb while putting many messages into a queue concurrently on a SMP server with 4 CPUs. Unfortunately we are not able to reproduce this reliably, but I would be happy to answer any question about the context. anonymous wrote : | 2006-08-25 20:07:15,376 ERROR [org.jboss.jms.server.endpoint.ServerConnectionEndpoint] Exception occured | javax.jms.IllegalStateException: Failed to acknowledge delivery null | at org.jboss.jms.server.endpoint.ServerConsumerEndpoint.acknowledgeTransactionally(ServerConsumerEndpoint.java:485) | at org.jboss.jms.server.endpoint.ServerConnectionEndpoint.processTransaction(ServerConnectionEndpoint.java:768) | at org.jboss.jms.server.endpoint.ServerConnectionEndpoint.sendTransaction(ServerConnectionEndpoint.java:380) | at org.jboss.jms.server.endpoint.advised.ConnectionAdvised.org$jboss$jms$server$endpoint$advised$ConnectionAdvised$sendTransaction$aop | (ConnectionAdvised.java:99) | at sun.reflect.GeneratedMethodAccessor83.invoke(Unknown Source) | View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=3967757#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...