JBoss Cache 2.x is not designed for use with JBoss AS 4.x. Certain elements of backward compatibility have been broken in 2.x, see the design forum and dev mail list archives for discussions around these decisions. You still need to use the jboss-cache.jar (which is JBC 1.4.x) that ships with JBoss AS 4.x for the clustering code in AS 4.x to work. You can, however, include JBC 2.x jars *in your application* (i.e., in your WAR or EAR) and use it from there. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4102927#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...