Hi, we have by now managed to find a work around, though we are still looking for a more elegant solution. So here is a short description of our current solution: We have now deployed a proxy application to the 4.2.0 server from which we have removed all annotations and which is configured with the following jboss.xml (and included in the ear): | <jboss> | <enterprise-beans> | <session> | <ejb-name>RmiProxy</ejb-name> | <jndi-name>ejb/remote/RmiProxy</jndi-name> | <invoker-bindings> | <invoker> | | <invoker-proxy-binding-name>stateless-rmi-invoker</invoker-proxy-binding-name> | </invoker> | </invoker-bindings> | </session> | </enterprise-beans> | </jboss> | Since there are no annotations, this application does not trigger the ejb3.deployer and is instead deployed as 2.x application in the 4.2.0 jboss. This proxy application is also configured to use the legacy rmi invoker. Now the 2.x client which is deployed in the 4.0.2 server can make 2.x style calls to the proxy which is deployed in the 4.2.0 server. The proxy application can then make rmi calls to the ejb3 application deployed in the same 4.2.0 server. This eliminates the problem with the 4.0.2 server not knowing the org.jboss.ejb3.stateless.StatelessRemoteProxy as the proxy application is running in a server that has the class and is itself configured as 2.x application which does not return ejb3 style rmi proxy objects. We're now looking for a way to eliminate the need for a proxy application. We may in the future simply try to upgrade the jboss on which the legacy application is running to remove this problem completely. Bye SPieper View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4153306#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...