Are you packaging any jar files containing the javax.ejb.* packages? If yes, then for a simple fix, remove them from your application packaging. They are already available in the the jar files under %JBOSS_HOME%/server/< serverName>/lib folder. For more details about classloading and issues that you might encounter because of the packaging, have a look at : http://wiki.jboss.org/wiki/Wiki.jsp?page=ClassCastExceptions http://wiki.jboss.org/wiki/Wiki.jsp?page=JBossClassLoadingUseCases http://wiki.jboss.org/wiki/Wiki.jsp?page=ClassLoadingConfiguration View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4135077#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...