For jbm 1.4, you need to read the release notes for the changes. Each minor release has some bug fixes, and they all back compatible with existing functionalities, by which it means you don't need to change your application code as long as you are using public APIs. You shouldn't use mixed version of JBM in runtime, as some of the libs need to be consistent, for example the jboss remoting jar. View the original post : http://www.jboss.org/index.html?module=bb&op=viewtopic&p=4242746#... Reply to the post : http://www.jboss.org/index.html?module=bb&op=posting&mode=reply&a...