I just encountered the same problem. Avoiding underscores in the broker name fixed it...
(see e.g. http://www.nabble.com/NPE-when-closing-tf1526855.html#a4284233) Holger -- View this message in context: http://www.nabble.com/Journal-is-already-opened-by-this-application-error-tf1329757.html#a5648310 Sent from the ActiveMQ - User forum at Nabble.com.
