Follow up -- I believe the problem is that JBoss 4.2.2 is now using a later version of Jaxb as part of the new web server implementation. Unfortunately, the new Jax bas rewritten almost the entire codeset, except for one or two classes that they completely rewrote, but kept the same name. One of these is what is causing my problem.
It would be quite an effort for us to rewrite the Jaxb things just to be able to go to 4.2.2 of JBoss; is there some way to poerhaps just go back to using the Tomcat web server so this isn't an issue?
You are running into typical classloader issues. You can configure your application to have scoped classloading. See these for more details