This is a very strange exception, since the existence of a marshaller for the "serializable" datatype is hard coded in Remoting. If you go to $JBOSS_HOME/server/$CONFIG/lib and type java -jar jboss-remoting.jar you'll get the version of Remoting. What is it? What version of the Application Server are you using? Have you changed the configuration of the EJB3 component in any way? Have you changed anything else? Strange ... View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4180355#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...