For the serial ID version error, this means that you are using two different jar in your application - the jar used by the client must be the exact same jar used by the server. Usually, you will want the client to use the jar files found in the "client" directory of the app server (copy that directory to the machine your client is running on). Changing a class within your application will not cause the app server to reload the class. You have to modify the timestamp on the primary descriptor, at which time the app server will redeploy the application. See http://wiki.jboss.org/wiki/Wiki.jsp?page=RedeployAnApplicationWhenChangeA.... Finally, this forum is for discussing the content of the O'Reilly book. Your questions belong in the Beginners Corner forum. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4054450#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...