When running ActiveMQ in embedded mode under WebSphere (I know that this is not a typical JEE-compliant deployment) the ObjectNames of the registered MBeans are modified by the container. Unfortunately, ActiveMQ fails to keep these names. As a result, ActiveMQ does not unregister its beans when an application is stopped, and a restart causes InstanceAlreadyExistExceptions.
The following change to ManagementContext.java may help:
but it should be something like: