That error means that you have used up your API quota for the day. See:

 1. [The "Throttles" documentation][1]
 2. [What are the API request limits? (FAQ)][2]
 3. [Request Throttling Limits (FAQ)][3]

Be sure you have and are using an application key, so that your quota is more than the default 300.  See the above links for more details on that too.


  [1]: https://api.stackexchange.com/docs/throttle
  [2]: http://stackapps.com/questions/67/how-api-keys-work
  [3]: http://stackapps.com/questions/1143/request-throttling-limits