An error occurred while trying to fetch data from your SharePoint site. Unexpected response from the server. The content type of the response is ''

Problema: Ao abrir Windows SharePoint Designer 2007/2010, aparece o seguinte erro:

An error occurred while trying to fetch data from your SharePoint site. Unexpected response from the server. The content type of the response is "". The status code is "OK"

Solução: Extend your web application Central Administration -> Application Management -> Manage Web Applications -> Select and click Extentd