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namespace Test
{
    class Program
    {
        static string useSalesWeb(String URL, String User, String Password, String XMLRequest)
        {
            String retval = String.Empty;

            try
            {
                WebRequest wreq = WebRequest.Create(URL);
                wreq.Method = "POST";
                wreq.Credentials = new NetworkCredential(User, Password);

                byte[] data = Encoding.ASCII.GetBytes(XMLRequest);
                Stream s = wreq.GetRequestStream();
                s.Write(data, 0, data.Length);
                s.Close();

                WebResponse wres = wreq.GetResponse();
                StreamReader sr = new StreamReader(wres.GetResponseStream());

                retval = sr.ReadToEnd();
            }
            catch (Exception ex)
            {
                retval = ex.Message;
            }

            return retval;
        }                    

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 byte[] data = Encoding.ASCII.GetBytes(XMLRequest);