Quick fix: upgrade to JDK 1.5. It includes Xerces instead of Crimson as the default JAXP implementation.
(Not so) slow fix: If I run your test under JDK 1.4 with the following classpath, it completes without any warning:
If I remove xercesImpl.jar, I get the warning.
I'm not sure what's in org.apache.xerces_2.7.0.jar. The Xerces 2.7.0 binary distribution does not include that file. It might be the source of the problem. Try removing it and see what happens.