Please refer to the following discussion for a detailed description of the problem: http://www.jboss.org/index.html?module=bb&op=viewtopic&t=158645 The problem is caused by the fact that at the time of xerces parser initialization, the context classloader is set to the war classloader while the current classloader is the deployer classloader. This leads to a ClassCastException because the various xerces classes are loaded by the 2 different classloaders mentioned. The solution is for JBossXB to set the context classloader to the current classloader before initializing xerces and then to restore the context classloader to its old value after the initialization is completed. I've seen numerous posts about this issue in the forums and none of the workarounds offered resolve the underlying problem. The solution must allow a war to bundle and use it's own version of the xerces jars without causing the app server to throw ClassCastExceptions. View the original post : http://www.jboss.org/index.html?module=bb&op=viewtopic&p=4249957#... Reply to the post : http://www.jboss.org/index.html?module=bb&op=posting&mode=reply&a...