After how many messages to the MDB does this exception occur? After 25 (=maxSessions)? Also, this looks incorrect to me: @ActivationConfigProperty(propertyName = "acknowledgeMode", propertyValue = "Auto-acknowledge") Should have been @ActivationConfigProperty(propertyName = "acknowledgeMode", propertyValue = "AUTO_ACKNOWLEDGE") View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4199109#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...