c＃WebClient Post返回服务器返回500，但是restclient正在工作

Question

This code returns a 500

string URL = "http://" + MSSRestSrv + ":8018/Quality/SerialNumbers/BoxBuilds/" + serial + "/Attach/";
string SubAssemblySerialNumber = form.serail;
string Refdes = row.Cells["RefDesc"].Value.ToString().Replace(";", "");

try
{
    using (WebClient client = new WebClient())
    {
        System.Collections.Specialized.NameValueCollection reqparm = new System.Collections.Specialized.NameValueCollection();
        reqparm.Add("SubAssemblySerialNumber", SubAssemblySerialNumber);
        reqparm.Add("Refdes", Refdes);
        byte[] responsebytes = client.UploadValues(URL, "POST", reqparm);
        string responsebody = Encoding.UTF8.GetString(responsebytes);
    }
}
catch (WebException we)
{
    MessageBox.Show(we.Response.ToString());
}

But via Chrome and Advanced Rest Client everything is 200 with this URL as POST

http://server:8018/Quality/SerialNumbers/BoxBuilds/999/Attach/?SubAssemblySerialNumber=555&Refdes=SUB1

Any ideas what's the difference?

This is working

string SubAssemblySerialNumber = form.serail;
string Refdes = row.Cells["RefDesc"].Value.ToString().Replace(";", "");
string URL = "http://" + MSSRestSrv + ":8018/Quality/SerialNumbers/BoxBuilds/" + serial + "/Attach/?SubAssemblySerialNumber=" + SubAssemblySerialNumber + "&Refdes=" + Refdes + "";
try
{
    using (WebClient client = new WebClient())
    {
        System.Collections.Specialized.NameValueCollection reqparm = new System.Collections.Specialized.NameValueCollection();

        byte[] responsebytes = client.UploadValues(URL, "POST", reqparm);
        string responsebody = Encoding.UTF8.GetString(responsebytes);
    }
}
catch (WebException we)
{
    MessageBox.Show(we.Response.ToString());
}

Answer 1

Thanks Martin Parkin

is is working

string SubAssemblySerialNumber = form.serail;
string Refdes = row.Cells["RefDesc"].Value.ToString().Replace(";", "");
string URL = "http://" + MSSRestSrv + ":8018/Quality/SerialNumbers/BoxBuilds/" + serial + "/Attach/?SubAssemblySerialNumber=" + SubAssemblySerialNumber + "&Refdes=" + Refdes + "";
try
{
    using (WebClient client = new WebClient())
    {
        System.Collections.Specialized.NameValueCollection reqparm = new System.Collections.Specialized.NameValueCollection();

        byte[] responsebytes = client.UploadValues(URL, "POST", reqparm);
        string responsebody = Encoding.UTF8.GetString(responsebytes);
    }
}
catch (WebException we)
{
    MessageBox.Show(we.Response.ToString());
}

Answer 2

    WebClient wc = new WebClient();
                wc.Headers.Add("Content-Type", "application/x-www-form-urlencoded");
                wc.Encoding = System.Text.Encoding.UTF8;
                wc.UseDefaultCredentials = true;
                string cRresultData = wc.UploadString(URI, "POST", CRreq);
                //string cRresultData = wc.UploadString(URI,CRreq);
                string cRresponse = "";

this code gives me  500 Server error