无法在Windows Phone中解析JSON

我正在尝试解析Json。我已成功将Json传递给字符串，但是无法将其转换为JObject。这是我的尝试代码：

private void webClient_DownloadStringCompleted(object sender, DownloadStringCompletedEventArgs e)
{
   string jsonStr = e.Result;
   if (!string.IsNullOrEmpty(jsonStr))
   {
      JObject objects = JObject.Parse(jsonStr); // this is when the error came at the first time. It says: An exception of type 'Newtonsoft.Json.JsonReaderException' occured in Newtonsoft.Json.DLL but was not handled in user code.
      JArray a = (JArray)objects[""];
      IList<Feeds.Topic> listFeeds = a.ToObject<IList<Feeds.Topic>>();
      this.DataContext = listFeeds;
   }
}

这是JSON的来源：http : //apibiru.herokuapp.com/v0.1/feeds/1? auth_token= 64d362d2e483e8023c46595f83ca8d9555ff6d7cc700a2474fbdbd341c43c1fb

感谢您的帮助，如果可以的话，谢谢:)