Stephen, We're getting same thing :)
Think we just figured things out -- our EAR had jms.jar and jboss-messaging-client.jar. We removed both of these just in case of classpath conflict and this message went away.
Give this a shot and see. Not sure if you have to remove BOTH of the jars, but this is what we did.
-Dustin
try to remove all jboss client jars but jbossall-client.jar !
it help me to solve the same problem(I use jboss 5.0 GA) !! good luck!