It looks like an incompatibility between Hibernate and GlassFish. In most cases, we generate this message when an application was undeployed (or redeployed) and someone still holding a reference to the old application's class loader is trying to load classes or resources from it. Emmanuel Bernard pointed me to the thread, so we have the right people involved to find the problem. could you answer the following questions : which version of glassfish and hibernate are u using ? thx, jerome View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4054992#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...