Error -The server committed a protocol violation in MVC 4

Hi everyone,

First, please you view my code use to upload file to mediafire


public static void uploadFile(string folder_key, HttpPostedFileBase file)
{
      System.Net.WebClient Client = new System.Net.WebClient();
      Client.Headers.Add("Content-Type", "binary/octet-stream");
      string filename = HttpContext.Current.Server.MapPath("~/Images/orderedList1.png");
      string UploadURI = "http://www.mediafire.com/api/upload/upload.php?session_token=" + token.session_token + "&uploadkey=" + folder_key + "&response_format=json";
      var request = (HttpWebRequest)HttpWebRequest.Create(UploadURI);
      var res = Client.UploadFile(UploadURI, "POST", filename);
}


- Red code have error below: "The server committed a protocol violation. Section=ResponseStatusLine". Althought, I inserted code below to web.config: 












- So how to fixed this error ? 

Thank you so very much.

Cheers.

Jimmy Mac.