http://www.example.org/check?uri=http://www.example.net/path/to/yourfile.html&lang=en
This case is clearly not valid. So the validator does the right job, except on port 8001.
http://www.example.org/check?uri=http://www.example.net/path/to/yourfile.html&lang=en
2002-07-10: Validator is ok... not sure it's correct see email to the list www-validator.