Try to realize, ot's not a JBoss problem. It is SUN problem that they allowed (after java 1.1) for same type classes not be be type safe if they are loaded by different clas loaders. Think about it; why should you be getting ClassCast exception on two classes with identical byte code?, but you will if class loaders are different. JBoss Class Loading architecture attempting to override this rule where com.foo.Foo=com.foo.Foo if they are the same version by making sure that the class is loaded only once by a single class loader and is shared by many applications. If you want to run appliations that are using different versions of the same packages, isolation could give you a way to do that, but you might also think about deploying such applications in different configurations of JBoss. Just copy "default" or "all" rrename it and there you have another instance that can host anoher version of Foo Regards View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4028320#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...