We're getting an identical error when an application deployed on JBoss422 tries to get a remote interface to an ejb that's deployed on JBoss404. I suspect that there has been a change in the org.jboss.ejb3.remoting.BaseRemoteProxy. We have an isolated class loader as default on our JBoss servers and if we put the jboss-ejb3-client.jar that is deployed on JBoss404 into the ear that is deployed on JBoss422 we no longer get the error. However, now we can't access 422 specific classes and get "JBossProxy not visible from the classloader" errors when trying to access the objects on the 422 server. It would seem that if you want to move from JBoss404 to 422, you will need to update ALL of the servers at the same time because of these incompatibilities. There doesn't seem to be any problem with using remote queues however. If anyone out there can tell me I'm wrong I'd be most pleased to know because for now I'm going to have to revert those servers running on 422 back to 404 until we can upgrade all at once. Thanks JBoss. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4125296#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...