You are attempting to serialize a session whose attribute map includes an object that is not serializable (RequestFacade). RequestFacade is the Tomcat implementation of HttpServletRequest -- mostly likely somewhere in your code you are storing a reference to the HttpServletRequest in some object and then placing that object in the session. That won't work for a clustered session, which needs to be serializable. Look at the usage of the nextapp.echo2.app.event.EventListenerList class. The stack trace shows that the RequestFacade is being serialized as part of an object graph that includes that class. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4152738#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...