in my case, I think the problem is, that the application finds 2 different versions of jsf-impl.jar (which includes com.sun.faces.config.WebConfiguration):* C:\Programme\jboss-4.2.0.GA\server\default\deploy\jboss-web.deployer\jsf-libs | * C:\Programme\jboss-4.2.0.GA\server\default\deploy\twentyfouract-ear.ear\twentyfouract.war\WEB-INF\lib | I removed the jsf-impl.jar from my .war and now it works see also: http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4130103#... View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4130106#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...