When using the rank API, I get the following error:

HTTP/1.1 500 Internal Server Error
Access-Control-Allow-Headers: *
Access-Control-Allow-Methods: : GET, POST, OPTIONS, DELETE
Connection: keep-alive
Content-Length: 126
Content-Type: application/json
Date: Thu, 23 Oct 2014 11:49:12 GMT
Server: Mashape/5.0.5
X-Ratelimit-Requests-Limit: 50
X-Ratelimit-Requests-Remaining: 49

{
  "status": 500,
  "code": 0,
  "message": "ws/palladian/retrieval/search/web/BlekkoSearcher",
  "link": "https://www.mashape.com/webknox/"

}