Why it dosent log in to the website ?

The code:

else if (dr == DialogResult.OK)
            {
                try
                {
                    username = lg.tb1;
                    password = lg.tb2;
                    StreamWriter w = new StreamWriter(appdir + txtfile);
                    w.WriteLine("User Name: " + username + Environment.NewLine + "Password: " + password);
                    w.Close();
                    CookieCollection cookies = new CookieCollection();
                    HttpWebRequest request = (HttpWebRequest)WebRequest.Create("http://www.tapuz.co.il");
                    request.CookieContainer = new CookieContainer();
                    request.CookieContainer.Add(cookies);
                    //Get the response from the server and save the cookies from the first request..
                    HttpWebResponse response = (HttpWebResponse)request.GetResponse();
                    cookies = response.Cookies;

                    string getUrl = "http://www.tapuz.co.il/Common/SignInPage.aspx?";
                    string postData = String.Format("email={0}&pass={1}", username, password);
                    HttpWebRequest getRequest = (HttpWebRequest)WebRequest.Create(getUrl);
                    getRequest.CookieContainer = new CookieContainer();
                    getRequest.CookieContainer.Add(cookies); //recover cookies First request
                    getRequest.Method = WebRequestMethods.Http.Post;
                    getRequest.UserAgent = "Mozilla/5.0 (Windows NT 6.1) AppleWebKit/535.2 (KHTML, like Gecko) Chrome/15.0.874.121 Safari/535.2";
                    getRequest.AllowWriteStreamBuffering = true;
                    getRequest.ProtocolVersion = HttpVersion.Version11;
                    getRequest.AllowAutoRedirect = true;
                    getRequest.ContentType = "application/x-www-form-urlencoded";

                    byte[] byteArray = Encoding.ASCII.GetBytes(postData);
                    getRequest.ContentLength = byteArray.Length;
                    Stream newStream = getRequest.GetRequestStream(); //open connection
                    newStream.Write(byteArray, 0, byteArray.Length); // Send the data.
                    newStream.Close();

                    HttpWebResponse getResponse = (HttpWebResponse)getRequest.GetResponse();
                    /*using (StreamReader sr = new StreamReader(getResponse.GetResponseStream()))
                    {
                        string sourceCode = sr.ReadToEnd();
                    }*/
                    
                    webBrowser1.Navigate("http://www.tapuz.co.il/Common/SignInPage.aspx?", "", byteArray, "Content-Type: application/x-www-form-urlencoded");
                }
                catch
                {
                    MessageBox.Show("error");
                }
            }

I see the log in screen in the webbrowser i enter my user name and password it dosent give any error or exception on my program and not in the webbrowser that the user name or password are not correct.

But it does nothing it seems like he get the user name and password but just loading again the log in screen.

I tried it yesterday with another site and it was working i only changed the links addresses.