Esto es rarisimo, una página tan conocida e importante como NatGeo.tv este caida, aca les dejo un extracto de la información que da:
Runtime Error
Description: An application error occurred on the server. The current custom error settings for this application prevent the details of the application error from being viewed remotely (for security reasons). It could, however, be viewed by browsers running on the local server machine.
Details: To enable the details of this specific error message to be viewable on remote machines, please create atag within a "web.config" configuration file located in the root directory of the current web application. This tag should then have its "mode" attribute set to "Off".