http://www.internetseer.com/help/error.xtp#codes
dice esto:
Server Error 5xx
Response status codes beginning with the digit "5" indicate cases in which the server is aware that it has erred or is incapable of performing the request. Except when responding to a HEAD request, the server SHOULD include an entity containing an explanation of the error situation, and whether it is a temporary or permanent condition. User agents SHOULD display any included entity to the user. These response codes are applicable to any request method.
500 Internal Server Error
The server encountered an unexpected condition, which prevented it from fulfilling the request.
Creo q has de revisar el codigo asp o en su caso la instalacion del IIS