Hi Kevin,
You have uncovered a bug in BisocketClientInvoker$PingTimerTask which allows a write after the task should have shut down, and I've created JIRA issue JBREM-1247 "BisocketClientInvoker$PingTimerTask NPE" to resolve it. However, I consider it a minor problem, since it occurs when a connection is shutting down anyway.
JBossMessaging has, throughout most of its history, turned off the bisocket transport ping facility by setting
<attribute name="pingFrequency" isParam="true">214748364</attribute>
in their remoting-bisocket-service.xml file. In fact, that's the value I see in JBossMessaging version 1.4.1.GA, which ships with EAP 5.0.1, so I don't understand why there would be any pinging going on. Did you change that parameter?
Anyway, I wouldn't worry about it.
As for the ConcurrentModificationException, you should post the issue on the JBossMessaging users forum.
-Ron