I know it's been a while, but my e-mail just got alerted about how much activity this thread has received. We have since removed JBoss Messaging clustering, and have reconfigured our MySQL to INNODB engine instead of NDBCLUSTER. We are only using a single, non-clustered JBoss 5.1.0 node. This single node holds up to our production traffic quite well. Perhaps just an ill-conceived clustering solution...