You need to do more searching of this forum. I answer variants of this question all the time. JBossCacheService serializes your session into a byte[] so it can send it over the network to replicate a copy to other nodes. If you store an object that is Serializable in the session's attribute map, JBossCacheService is going to throw an exception when it tries to serialize the session. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4163100#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...