Well, that's the reason! Looks like some of the classes are being loaded from JBoss's jar (the one from server/default/lib) and some from your application's package. I would suggest, enabling classloader scoping for your EAR, which should solve this problem. Just add a jboss-app.xml file in the META-INF folder of the EAR with something like this: | <jboss-app> | | <loader-repository> | org.myapp:loader=MyAppClassLoader | <loader-repository-config>java2ParentDelegation=false</loader-repository-config> | </loader-repository> | | | </jboss-app> More details can be found at http://wiki.jboss.org/wiki/Wiki.jsp?page=ClassLoadingConfiguration View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4124410#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...