xmlrpc.php error in HTML Validation Results @ http://www.htmlhelp.com/

Hi, I have this kind of validation error with this file, it’s a default one, so I dont know whats wrong with it.

Document Checked
URL: http://www.website.com/xmlrpc.php
Character encoding: windows-1251
Level of HTML: Unknown
Errors and Warnings
Line 1, character 1:
XML-RPC server accepts POST requests only.
^Error: missing document type declaration; assuming HTML 4.01 Transitional

Line 1, character 1:
XML-RPC server accepts POST requests only.
^Error: text is not allowed here; try wrapping the text in a more descriptive container

Line 1, character 43:
… r accepts POST requests only.
^Error: HTML not finished but document ended

BTW. is it possible to validate ATOM? thx.