Those $Proxy cast exceptions are an indication of a problem with your client Classpath.
Note what Tim said above:
2) I'm using the JBossWS version included in the jboss 5.1.0 build
3) I resolved the class path issue by only including the jars found in de wsrunclient file, plus the ones from the endorsed jboss dir as well as setting the java endorsed library to that same location.
It is important that the java.endorsed.dirs property be set to the endorsed directory of your JBoss distribution.