ここにいくつかのコードがあります:
var client = new WebClient();
client.BaseAddress = "http://localhost/";
client.Headers["Content-type"] = "application/x-www-form-urlencoded";
client.Proxy = null;
// The server gets the data
var responseStr = client.UploadString(url, data);
...
// The server gets an empty post data
responseStr = client.UploadString(url, data);
Webclient は使い捨てのはずですか?