Is it possible that you have one of these jars: jaxb-core.jar, jaxb-impl.jar or jaxws-rt.jar/wsit-rt.jar inside your userlib directory? If this is the case, try to delete them and retry. My hunch is that you have a redundant (Metro) library on your classpath.
If this doesn't help and no other forum members have a solution, I suggest you file a ticket.
I looked into the WSDL recently and I have a workaround for this issue in case someone else encounter this WS-Security error.
Background: When the WS Security policy exist, Metro library expect a SecurityHeader object containing the security information. In Mendix, WS Security is provided in custom template and send as is. Therefore, Metro library throws exception.
The workaround: Since we don't handle the policy. I suggest to remove the policy. The WS-Security will still work.