You can code up an implementation of javax.servlet.http.HttpSessionAttributeListener that tries to serialize each attribute when the attributeAdded or attributeReplaced callbacks are called. If serialization fails, log the attribute name and the stack trace. Then tweak your web.xml to include the listener. Use in dev environment only of course. I wrote such a thing a while back; it could also descend into collections to try to find any offending collection element. But I can't find it. Ignoring the descending into collections part, it's pretty easy to do, so you could code one up. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4012563#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...