Refused to display 'site' in a frame because it set 'X-Frame-Options' to 'sameorigin'

En global.asax, agregar:

AntiForgeryConfig.SuppressXFrameOptionsHeader = true;

En web.config:

  <system.webServer>
    <httpProtocol>
      <customHeaders>
        <add name="X-Frame-Options" value="AllowAll" />
      </customHeaders>
    </httpProtocol>
  </system.webServer>