What version of jboss are you using?
I swedish guy tested to get it to work with 2.4.3, but it was not possible, even with a number of changes.
2.4.4, should be another story though...
I'm using 2.4.4 - though I had exactly the same error on 2.4.3 but it was reported as coming from the JBoss side as opposed to the Sonic side. Is it something to do with the session pool that is passed in?