JBoss provides myfaces at the system level. When you duplicate system-level JARs in your application, you can run into all sorts of problems when classes loaded from one classloader interact with ones loaded from another. I don't know which classes are coming from which classloader, but that's not that important. The important thing is to know not to do it. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=3994845#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...