It's not clear to me what's going on in the messages you log. Apparently JGroups is reading a packet(s) with null data; that's what's causing the NPEs mentioned in the error messages. Perhaps this is preventing the threads associated with the UDP protocol stopping properly. But what the root issue is I don't know. Can you try a more recent JGroups release? Basically any subsequent release is compatible with JBC 1.3.0.SP2, so I'd say try 2.4.1. (See http://labs.jboss.com/portal/jbosscache/compatibility/index.html for compatibility listings.) View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4011124#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...