You put org.hibernate.impl.ScrollableResultsImpl in HttpSession (which is replicated on cluster). ScrollableResultsImpl is not Serializable but replication requires this. Try to put in session something like list not scroll from hibernate and all objects in this lists also must be serialized - clustering world of java ;) There are some solution which doesn't requires Serializable in replication but it is other topic. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4170955#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...