我正在尝试通过 POST 方法将数据上传到 REST 服务，但由于某些原因，服务器告诉我：
System.Net.WebException：远程服务器返回错误：NotFound。
我正在尝试使用以下代码上传数据：
WebClient addserving = new WebClient();
addserving.Credentials = new NetworkCredential(username.Text, passwort.Password);
addserving.Encoding = System.Text.Encoding.GetEncoding("ISO-8859-1");
addserving.Headers[HttpRequestHeader.ContentType] = "application/x-www-form-urlencoded";
addserving.UploadStringAsync(new Uri("http://jokr.info/api/v8/diary/add_item.xml&apikey=123456&item_id=1240&serving_id=1566"), "POST");
addserving.UploadStringCompleted += new UploadStringCompletedEventHandler(serving_UploadStringCompleted);
API的文档告诉我这样发布：
Rate Limit: Yes
HTTP Methods: POST
Authentication: Basic authentication (Username or E-Mail and Password)
Formats: xml
Parameters: format, apikey [GET], activity_id [POST], activity_duration [POST], activity_kj [POST], timestamp [POST] (optional)
有谁知道出了什么问题？