This may just be a problem with jboss-serialization.jar and nothing to do with JBoss Cache at all. Clebert's investigating the potential problem with jboss-serialization. http://jira.jboss.com/jira/browse/JBSER-89 FYI, JBoss Cache 1.4.0.GA and 1.4.0.SP1 both ship with jboss-serialization-1.0.1.GA. The potential upside is that if it is a bug in jboss-serialization, fixing the issue will just be upgrading the one jar, and it should be backward-compatible with JBoss Cache 1.4.0.XX. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=3971076#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...