Thanks for your reply! :) It's container managed. The MDBs do nothing in the testing environment. The error message is shown below: java.sql.SQLException: null, message from server: "Deadlock found when trying to get lock; try restarting transaction" org.jboss.resource.adapter.jdbc.WrappedPreparedStatement.executeUpdate(WrappedPreparedStatement.java:251) at org.jboss.mq.pm.jdbc2.PersistenceManager.remove(PersistenceManager.java:1401) at org.jboss.mq.server.BasicQueue.acknowledge(BasicQueue.java:749) at org.jboss.mq.server.JMSTopic.acknowledge(JMSTopic.java:349) I got this exception even though both parameters MaximumSize and MinimumSize of container invoker "message-driven-bean" set to 1 and MDB container parameter "MaximumSize" set to 1 with "strictMaximumSize" set to true View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=3991193#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...