Well, I got there in the end. For the benefit of anyone else who has this problem: The reason is that the classloader for the ejb interface was not the same as that of the ejb class. So: remove the interface file from the war. if, in the ear jboss-app.xml you have: <loader-repository> onebox:app=backend </loader-repository> or something similar, remove it. And you should be OK. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4050397#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...