我试图使用网络浏览器控制自动登录到一个网站论坛，但它永远不会登录什么可能是错误的

这是登录的链接:

登录

如果我试图在web浏览器手动登录，它什么也不做，但打开一个弹出消息问我是否要关闭窗口，我点击是，什么都没有发生。在普通的chrome浏览器，而不是在web浏览器中，当我输入用户名和密码，并点击登录，它也关闭了窗口的登录自动刷新页面，我登录。但是通过浏览器它永远不会登录。它不给出任何错误或异常，只是什么也不做。

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Net;
using System.IO;
using System.Text.RegularExpressions;
using System.Runtime.InteropServices;
using System.Security.Permissions;
namespace Champinos
{
    public partial class Form1 : Form
    {
        WebClient webc = new WebClient();
        string url = "";
        string username = "";
        string password = "";
        string commit = ""; //this matches the data from Tamper Data
        private int timeElapsed;
        private string newline1 = "";
        private bool complete;
        private int count;
        public Form1()
        {
            InitializeComponent();
            timeElapsed = 1;
            label3.Visible = false;
            label5.Visible = false;
            complete = false;
            count = 1;
        }
        void webBrowser1_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e)
        {
            url = "http://www.tapuz.co.il/Common/SignInPage.aspx?backUrl=http://www.tapuz.co.il/Common/SignIn.aspx@loginDone=1";
            username = "yasonikolados";
            password = "ynnad1972";
            commit = "Login";//"Sign+In";
            label1.Text = "Completed";
            string source = "";
            source = webc.DownloadString("http://www.tapuz.co.il/forums2008/forumpage.aspx?forumid=393&r=1");
            string start = "data-token=";
            string end = " href";
            int firstTag = source.IndexOf(start);
            int lastTag = source.IndexOf(end, firstTag);
            int startIndex = firstTag + start.Length + 1;
            int endIndex = lastTag;
            string authenticityToken = source.Substring(startIndex, endIndex - startIndex - 30);
            webBrowser1.DocumentCompleted -= webBrowser1_DocumentCompleted;
            webBrowser1.DocumentCompleted += webBrowser1_DocumentCompleted2;
            string postData = string.Format(
                "authenticity_token={2}&session" + 
                "[username_or_email]={0}&session[password]={1}&commit={3}",
                  username, password, authenticityToken, commit);
            ASCIIEncoding enc = new ASCIIEncoding();
            webBrowser1.Navigate("http://www.tapuz.co.il/Common/SignInPage.aspx?backUrl=http://www.tapuz.co.il/Common/SignIn.aspx@loginDone", "", enc.GetBytes(postData), "Content-Type: application/x-www-form-urlencoded'r'n");
        }
        private void Form1_Load(object sender, EventArgs e)
        {
            webBrowser1.ScriptErrorsSuppressed = true;
            webBrowser1.DocumentCompleted += webBrowser1_DocumentCompleted;
            webBrowser1.Navigate("http://www.tapuz.co.il/forums2008/forumpage.aspx?forumid=393&r=1");
        }
        private void webBrowser1_DocumentCompleted2(object sender, WebBrowserDocumentCompletedEventArgs e)
        {
            WebBrowser b = sender as WebBrowser;
            string response = b.DocumentText;
            if (response.Contains("Sign out"))
            {
                MessageBox.Show("Login Successful");
            }
        }       
    }
}