I just realized what's going on -- when you call put(fqn, key, value) or remove(fqn, key, value), when the call replicates, the old value is returned. That's why foo.MyBadObject is included with the response and can't be deserialized. The old value really shouldn't be returned -- it's just discarded. This is fixed in 1.4.1 which should be out in a few weeks -- see http://jira.jboss.com/jira/browse/JBCACHE-766. Luckily for you, when JGroups has trouble deserializing the response, it just logs the error and treats the response as null. IMHO that's a bug, but in this case it works to your benefit, since JBC is expecting a null. A workaround until 1.4.1 is out is to just suppress ERROR logging from the org.jgroups.blocks.GroupRequest category. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=3983627#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...