I created a new project from scratch and the exception has gone away. I believe that the reason is that I was using a synchronous-only interface on the server side. The service endpoint interface code for the server was generated WITHOUT using: <enableAsyncMapping>true</enableAsyncMapping> For the client I re-ran wsconsume and generated a SEI with asynchronous mapping enabled. Unfortunately I placed the SEI in my EAR's /lib folder and forgot to update it. Asynchronous invocation now works but the messages are delivered out-of-order. I will create a new post for that... View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4170082#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...