404 Not Found

Something's gone wrong.

RFC2068 says:

10.4.5 404 Not Found

   The server has not found anything matching the Request-URI. No indication
   is given of whether the condition is temporary or permanent.

   If the server does not wish to make this information available to the
   client, the status code 403 (Forbidden) can be used instead. The 410
   (Gone) status code SHOULD be used if the server knows, through some
   internally configurable mechanism, that an old resource is permanently
   unavailable and has no forwarding address.

Source: Hypertext Transfer Protocol -- HTTP/1.1 (RFC2068); R. Fielding, J. Gettys, J. Mogul, H. Frystyk, T. Berners-Lee; January 1997.