You shouldn't need to copy anything. This error occurs because the user is attempting to start a clustered post office in a non clustered JBoss configuration. E.g. user is trying to start JBM clustered in the "default" configuration. He should be using the "all" configuration. In the "all" configuration, jgroups.jar is already present. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4186110#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...