Ｗ３Ｃの検証サービスで検証をしていて↓のようなメッセージが出てきた場合は

You have requested we check the referring page, but your browser
did not send the
HTTP "Referer" header field. This can be for several reasons,
but most commonly it is
because your browser does not know about this header,
has been configured not to send
one, or is behind a proxy or firewall that strips it
out of the request before it
This is not an error in the referring page!
Please use the form interface on the Validator Home Page to
check the page by URL.

または

Sorry, this type of URL scheme (undefined) is not supported by this service.
Please check that you entered the URL correctly.
URLs should be in the form: http://validator.w3.org/
URLs should be in the form: http://validator.w3.org/as outlined on our
Feedback page.
Make sure to include the specific URL you would like us to support, and
if possible
provide a reference to the relevant standards document describing
the URL scheme in question.
Remember that you can always save the page to disk and Validate it using
the File Upload interface.

[解決方法]

「ＶａｌｉｄａｔｅｂｙＵＲＬ」で、アップロードすると解決します。