Using http://validator.w3.org/checklink of W3 in a site (www.fox.com.uy) to verify outgoing links I saw that when trying to access to an external site (of my property) in a different server Windows gives the following error me:

List of broken links and redirects: http://www.enbuscadores.net
What to do: The Link is forbidden! This needs fixing. Usual suspects: to missing index.html or Overview.html, or to missing ACL. HTTP Code returned: 403 HTTP Message: Forbidden
Somebody knows how can I correct this error?
It happens if I scan in any other site that contains a Link to my site (enbuscadores)

Thanks and regards
Martin