Well, I did the main class with the test "isAssignableFrom" inside and it returns true. As you said, it probably means that there is a classLoader incompatibility with JBP 2.6.1 and my app. I did an other test: I tried to deploy my new EAR for JBP 2.6.1 (with myfaces-api.jar and myfaces-impl.jar in WEB-INF/lib and the parameter org.jboss.jbossfaces.WAR_BUNDLES_JSF_IMPL (= true) in the web.xml) in JBP 2.6.0 CR2 + JB 4.0.5 GA. I have the same error whereas it works when I don't put the jars in the WAR. I think that my problem comes from the fact I had to put the myFaces jars in my application war to use Myfaces with JBP 2.6.1GA. But I don't know how to do differently... View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4070176#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...