This has been sorted out as an error in the application being upgraded. Apparently the earlier JMX libraries did not test (at least in the same way as the libraries shipped with JDK 1.5) whether the MBean to which a NotificationListener was being added was an implementation of NotificationBroadcaster. The test is done in the MBeanServer.isInstanceOf(), not by looking at the class of the MBean (which was appropriate in the app) but at the class name recorded in the MBeanInfo, which was incorrectly entered in this app and did not match the class of the MBean. Hope this info is of use to someone else. Jeff View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4083563#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...