Going by the exception stacktrace, it seems to be failing (going into indefinite loop) while serializing this list contents: anonymous wrote : private List groups = new ArrayList(0); Try playing around with the list contents or by commenting out this list from the user and see if there is any difference. Irrespective of the outcome, there shouldn't have been an indefinite loop in first place. Since the stacktrace shows the org.jboss.serial.persister.RegularObjectPersister, i think you should report this in the "Design of JBoss Serialization" forum http://www.jboss.com/index.html?module=bb&op=viewforum&f=233. I know its a design forum meant for design discussions, but i could not find a user forum where you could open a new thread. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4191462#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...