Different classloaders - I think that must be it. I guess it is different classloaders, the Tomcat one loading the webapp and another JBoss one loading the JAR. And thanks for the warning - I think I will skip the custom type and just put a Map in the cache with nothing else than Strings and Integers and such. Anyway, I wonder how to solve this classloading issue. Since the class is used by the webapp, it is in a JAR in WEB-INF/lib. But if it is only there, the cache cannot find it when it tries to deserialize the object. So were should I put the class? Is this possible at all? Thanks! Torsten View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4093429#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...