In general, you should not count on being able to replace/override core Java EE classes in your application. I don't know anything about XFire, but I do know that code that is intended to be run in a Java EE server should NOT have their own copy of the annotations. So, don't add the annotation classes to your application. If there is a version compatibility between the annotations you need to either find the correct version of XFire for the Java EE version in JBoss or update jbossws.sar in JBoss to a version that works with XFire. However, in saying that, I really find it hard to believe that they are using incompatible versions of the annotations. Are you sure the problem wasn't simply that you were providing an equivalent class with your application, causing some classloader confusion? There are still some classloading tricks that might make this work, but it's better not to go there. Could you show your packaging so we can make sure the problem isn't just a simple packaging problem. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=3995907#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...