Good news. I was able to test this scenario on WebSphere today. It looks like the only thing we need to do in JBossCache is catch the registration error. So the typical failure mode is as follows - Someone in a standalone environment starts a cache instance using the default name (e.g., TreeCache-Group). On WebSphere, the instance is registered with a name like jboss.cache:service=TreeCache-Group, server=websphere.... If the same instance tries to register again, we use the actual registration name and detect that this is an attempt to register again. If another instance (e.g., another standalone cache application) is then started and uses the default name, the code to detect a current registration won't detect that the name is already in use because it will use the default name (i.e., because serviceName is null at this point). The registration attempt will proceed and fail with the InstanceAlreadyExists exception because the actual name is already in use. So the fix is to simply catch the exception and report it as a warning. Note that this doesn't change the JMX availability of the cache's mbean. The mbean is registered to the first client to use the name. Unless I find anything further while looking at deregistration, I'll just fix this by handling the exception. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4038986#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...