I finally found the problem after 24 hours of pain! The root cause was an @Email hibernate validation - it appears that in earlier versions of hibernate validator there are problems with using @Email on an optional email property as jsf passes an empty string rather than a null and so you can pass the screen validation but then get an error on persist. This has subsequently been fixed but as I am using the default hibernate version provided by Jboss AS and this is different on my dev server (JBoss Studio 2.0 BETA bundled with JBoss AS) and my PROD server (JBoss AS 4.2.3GA). I am going to look into using classloaders to ensure the app I deploy has the correct jars I depend on. In the meantime, I will upgrade my server to use a new version of hibernate. View the original post : http://www.jboss.org/index.html?module=bb&op=viewtopic&p=4227707#... Reply to the post : http://www.jboss.org/index.html?module=bb&op=posting&mode=reply&a...