After more searching and testing we came upon a Thread that suggested that the problem was related to having the onMessage() method within the WebContainer (in the application we are currently porting the .war file creates a singleton via the ServletContextListener which receives the JMS message notifications). http://www.jboss.org/index.html?module=bb&op=viewtopic&t=144634 To test this out, we extracted a simple test case that creates a JMS subscriber and registers itself as a MessageListener on the topic. This MessageListener is a simple service created with the @Service annotation and it also experiences the same class cast exceptions when running within the same JBoss5 instance as the Topic to which it subscribes. I realize that we could use MDB's for this process and have them pass the data they receive into an injected service/EJB, etc. However, not all of our client applications run in JBoss (some run in Tomcat and others are standalone Java processes) and we share client libraries across them. Ideally we would prefer not to have to do something different for our JBoss applications (especially since it works if the clients are on different JBoss servers already). View the original post : http://www.jboss.org/index.html?module=bb&op=viewtopic&p=4230207#... Reply to the post : http://www.jboss.org/index.html?module=bb&op=posting&mode=reply&a...