Did you ever figure this out or get an answer? I have the same problem "all of a sudden" EJB3 CMP entity beans are failing with the same error you had " javax.ejb.EJBException: java.lang.IllegalArgumentException: Unknown entity: __" when I call em.persist(MyCMPBean) from the session bean. Don't think it matters but... the Session Bean is a Stateless EJB as a webservice. All beans are done with annotations. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=3972123#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...