C#验证码模拟登录的时候下载到的验证码错误
大家帮忙啊，我最近在搞C#验证码模拟登录，登录联通网上营业厅。http://wwww.10010.com/login.jsp
我采用半自动的方式下载到验证码，然后自己填写，然后提交，可是返回值总说验证码错误，请大侠指教啊！

 //模拟登录

        private void btnLogin_Click(object sender, EventArgs e)

        {

            string checkCode = textValidateCode.Text;

            string postUrl = "http://www.10010.com/login/userLogin.action";

            string postData = "loginInfo.userName=手机号&loginInfo.password=密码&loginInfo.check_code=" + checkCode + "&loginInfo.UniTokenRequest=null&loginInfo.returnURL=&loginInfo.areaNumber=&loginInfo.loginType=01&MobileUserName=手机号&loginInfo.identifyType=01&MobilePassword=密码&RandomPassword=&MobileCheckCode=" + checkCode + "&FixAreaNumber=%D6%D0%CE%C4%2F%C6%B4%D2%F4&FixUserName=%CE%DE%D0%E8%CA%E4%C8%EB%C7%F8%BA%C5%A3%A1&FixPassword=&FixCheckCode=%B5%E3%BB%F7%BB%F1%C8%A1&TeleAreanumber=%D6%D0%CE%C4%2F%C6%B4%D2%F4&TeleUserName=%CE%DE%D0%E8%CA%E4%C8%EB%C7%F8%BA%C5%A3%A1&TelePassword=&TeleCheckCode=%B5%E3%BB%F7%BB%F1%C8%A1&ADSLAreaNumber=%D6%D0%CE%C4%2F%C6%B4%D2%F4&ADSLUserName=%CE%DE%D0%E8%CA%E4%C8%EB%C7%F8%BA%C5%A3%A1&ADSLPassword=&ADSLCheckCode=%B5%E3%BB%F7%BB%F1%C8%A1&LANAreanumber=%D6%D0%CE%C4%2F%C6%B4%D2%F4&LANUserName=%CE%DE%D0%E8%CA%E4%C8%EB%C7%F8%BA%C5%A3%A1&LANPassword=&LANCheckCode=%B5%E3%BB%F7%BB%F1%C8%A1&WebUserName=%C4%FA%D7%A2%B2%E1%B5%C4%D3%CA%CF%E4&WebPassword=&WebCheckCode=%B5%E3%BB%F7%BB%F1%C8%A1";

            //string ydData="submitMode=2&ErrorUrl=..%2FbriefLogon.do&ReturnURL=www.sd.10086.cn%2Fportal%2Fgxhzq%2Findex.jsp&FieldID=1&entrance=IndexBrief&mobileNum=手机号&logonMode=1&servicePWD=******&randCode="+checkCode+"&smsRandomCode=";

            string strr = Http.GetHtml(postUrl, postData, aspcookie, out header);

            FileStream fst = new FileStream("D:\\0.htm", FileMode.Append);

            StreamWriter swt = new StreamWriter(fst, Encoding.GetEncoding("utf-8"));

            //写入

            swt.WriteLine(strr);

            swt.Close();

            fst.Close();



        }

        //下载验证码

        private void btnGetCode_Click(object sender, EventArgs e)

        {

            HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create("http://www.10010.com/getImage.jsp");

            request.CookieContainer = co;

            HttpWebResponse response = (HttpWebResponse)request.GetResponse();