Have solved the problem. Actually job.class was out in server\all\lib and also in e1 EAR. So when I was checking for isAssignableFrom , the class versions were different as classloaders were different and isolation ear was enabled using jboss_app.xml. I removed job.class from e1 ear and now have just one copy in lib and no other module will have it. isAssignableFrom is returning correct value. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4149296#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...