I'm using EJB3 as is provided with GlassFish. I think the biggest factor was the Identity instance I'll go back to check if there are any others. When you enable availability on an application for a GlassFish cluster you get in memory session data replication across the cluster. As a result what is stored for session data needs to be Serializable. I noticed a Serializable exception being thrown pertaining to the Identity when it was attempted to replicate it although it does implement the Serializable interface. Perhaps there is some additional session state data that is not Serializable. All the ones that are outjected in our code are as far as I can tell. S.D. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4108273#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...