Log in server with HttpwebRequest post mode

public string BeginPostSend(string posturl, 
    Encoding encoding,
    string UserAgent,
    string Accept,
    string AcceptLanguage,
    string proxyURL,
    string postData)
{
    string contentResult = string.Empty;
    string err = string.Empty;
    int couterTry = 0;
          
    byte[] data = encoding.GetBytes(postData);
    char[] charArray = new char[2048];

    do
    {
        // Set some request parameter
        // So as to readability, don't put below parameter set into a lonely function  
        this.request = WebRequest.Create(posturl) as HttpWebRequest;

        this.request.CookieContainer = this.cookieContainer;
        this.request.AllowAutoRedirect = true;
        this.request.Method = "POST";
        this.request.Accept = Accept;
        this.request.Headers.Add("Accept-Language", AcceptLanguage);
        this.request.Headers.Add("Accept-Encoding", "gzip, deflate");
        this.request.CachePolicy = new System.Net.Cache.RequestCachePolicy(System.Net.Cache.RequestCacheLevel.NoCacheNoStore);
        this.request.KeepAlive = true;
        this.request.ContentLength = data.Length;
        this.request.ContentType = "application/x-www-form-urlencoded";
        this.request.UserAgent = UserAgent;
        this.request.Timeout = 60000;

        //Define a Proxy Object
        WebProxy proxy = new WebProxy();
        //Server address and port                          
        proxy.Address = new Uri(proxyURL);
        //User and Password                         
        //proxy.Credentials = new NetworkCredential("", "");
        //Launch web Authentication
        this.request.UseDefaultCredentials = true;
        //Set proxy                
        this.request.Proxy = proxy;

        try
        {
            couterTry++;

            if (couterTry > 1)
            {
                Thread.Sleep(6000);
            }

            // Put post data into stream
            this.outStream = request.GetRequestStream();
            this.outStream.Write(data, 0, data.Length);

            // Send request and get relative response data
            using (this.response = request.GetResponse() as HttpWebResponse)
                using (this.inStream = this.response.GetResponseStream())
                    using (this.SR = new StreamReader(this.inStream, encoding))
                    // Not untill request.GetResponse(), program begin sending Post request to destination Web page 
                    {
                        if (this.response.StatusCode == HttpStatusCode.OK)
                        {
                            streamDelegate SRDelegate = new streamDelegate(this.SR.ReadToEnd);

                            try
                            {
                                IAsyncResult asyncR = SRDelegate.BeginInvoke(null, null);
                                asyncR.AsyncWaitHandle.WaitOne();
                                contentResult = SRDelegate.EndInvoke(asyncR);
                            }
                            catch 
                            {
                                this.DisposeStream();
                                continue;
                            }

                            //contentResult = tempResult.ToString();
                            this.DisposeStream();
                            break;
                        }
                        else
                        {
                            this.DisposeStream();
                            contentResult = string.Empty;

                            if (couterTry >= 10)
                            {
                                break;
                            }
                        }
                    }
                }
                catch (Exception ex)
                {
                    this.DisposeStream();
                    contentResult = string.Empty;
                    err = ex.Message;

                    if (couterTry >= 10)
                    {
                        break;
                    }
                }

            } while (true);

            this.DisposeStream();

            return contentResult;
        }