WebRequest类实现模拟IE发帖到百度贴吧,百度贴吧判断为广告贴,求解

using System;
using System.Collections.Generic;
using System.Collections.Specialized;
using System.Text;
using System.Net;
using System.IO;

namespace baidupost
{
    class SendtoBaiduTieba
    {
        public static void fatie(string username, string password, string title, string content, string word, out string loginState, out string sendState)
        {
            CookieContainer cookieContainer = new CookieContainer();
                
            // 设置打开页面的参数
            string URI = "https://passport.baidu.com/?login";
            HttpWebRequest request = WebRequest.Create(URI) as HttpWebRequest;
            request.ContentType = "application/x-www-form-urlencoded";
            request.Method = "POST";
            request.Accept="application/x-shockwave-flash, image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, application/vnd.ms-excel, application/vnd.ms-powerpoint, application/msword, */*";
            request.UserAgent = "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1;  Embedded Web Browser from: http://bsalsa.com/; .NET CLR 2.0.50727; CIBA)";
            request.KeepAlive = true;


            // 接收返回的页面
            HttpWebResponse response = request.GetResponse() as HttpWebResponse;
            Stream responseStream = response.GetResponseStream();
            StreamReader reader = new StreamReader(responseStream, Encoding.GetEncoding("GB2312"));
            string srcString = reader.ReadToEnd();

            ///////////////////////////////////////////////////
            // 2. 自动填充并提交 登陆 页面
            ///////////////////////////////////////////////////

            // 用户名和密码

            // 将文本转换成 URL 编码字符串
            username = System.Web.HttpUtility.UrlEncode(username, Encoding.GetEncoding("GB2312"));
            word = System.Web.HttpUtility.UrlEncode(word, Encoding.GetEncoding("GB2312"));

            // 要提交的字符串数据。格式形如:
            string formatString =
                     "tpl_ok=&next_target=&tpl=&skip_ok=&aid=&need_pay=&need_coin=&pay_method=&u=.%2F&return_method=get&more_param=&return_type=&psp_tt=0&username={0}&password={1}";
            string postString =
                     string.Format(formatString, username, password);

            // 将提交的字符串数据转换成字节数组
            byte[] postData = Encoding.ASCII.GetBytes(postString);

            // 设置提交的相关参数
            request = WebRequest.Create(URI) as HttpWebRequest;
            request.Method = "POST";
            request.ContentType = "application/x-www-form-urlencoded";
            request.CookieContainer = cookieContainer;
            request.ContentLength = postData.Length;
            request.Accept = "application/x-shockwave-flash, image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, application/vnd.ms-excel, application/vnd.ms-powerpoint, application/msword, */*";
            request.UserAgent = "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1;  Embedded Web Browser from: http://bsalsa.com/; .NET CLR 2.0.50727; CIBA)";
            request.KeepAlive = true;

            // 提交请求数据
            System.IO.Stream outputStream = request.GetRequestStream();
            outputStream.Write(postData, 0, postData.Length);
            outputStream.Close();

            // 接收返回的页面
            response = request.GetResponse() as HttpWebResponse;
            request.CookieContainer = cookieContainer;
            responseStream = response.GetResponseStream();
            reader = new StreamReader(responseStream, Encoding.GetEncoding("GB2312"));
            srcString = reader.ReadToEnd();
            if (srcString.IndexOf("location.href=url") > 1)
                loginState = "登陆成功!\r\n";
            else
                loginState = "登录失败\r\n";
            ///////////////////////////////////////////////////
            // 3. 打开 发帖 页面
            ///////////////////////////////////////////////////
            // 设置打开页面的参数

            URI = "http://tieba.baidu.com/f?kw=" + word;
            request = WebRequest.Create(URI) as HttpWebRequest;
            request.ContentType = "application/x-www-form-urlencoded";
            request.Accept = "application/x-shockwave-flash, image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, application/vnd.ms-excel, application/vnd.ms-powerpoint, application/msword, */*";
            request.UserAgent = "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1;  Embedded Web Browser from: http://bsalsa.com/; .NET CLR 2.0.50727; CIBA)";
            request.KeepAlive = true;
            request.Method = "GET";
            request.CookieContainer = cookieContainer;
            // 接收返回的页面
            response = request.GetResponse() as HttpWebResponse;
            responseStream = response.GetResponseStream();
            reader = new StreamReader(responseStream, Encoding.GetEncoding("GB2312"));
            srcString = reader.ReadToEnd();
            // 获取发帖所需参数 这里使用正则表达式获取 
            int formStart = srcString.IndexOf("return f_submit()", 0);
            int formEnd = srcString.IndexOf("</form>", formStart);
            string htmlForm = srcString.Substring(formStart, formEnd - formStart);
            string ct = FormatHtml.FormatHtmlCode(htmlForm, "<input type=hidden name=ct value=(?<key>.*?)>");
            string tn = FormatHtml.FormatHtmlCode(htmlForm, "<input type=hidden name=tn value=(?<key>.*?)>");
            string lm = FormatHtml.FormatHtmlCode(htmlForm, "<input type=hidden name=lm value=\"(?<key>.*?)\" >");
            string z = FormatHtml.FormatHtmlCode(htmlForm, "<input type=hidden name=z value=(?<key>.*?)>");
            string sc = FormatHtml.FormatHtmlCode(htmlForm, "<input type=hidden name=sc value=(?<key>.*?)>");
            string cm = FormatHtml.FormatHtmlCode(htmlForm, "<input type=hidden name=cm value=\"(?<key>.*?)\">");
            string bs = FormatHtml.FormatHtmlCode(htmlForm, "<input type=hidden name=bs value=\"(?<key>.*?)\">");
            string str2 = FormatHtml.FormatHtmlCode(htmlForm, "<input type=hidden name=str2 value=\"(?<key>.*?)\">");
            string str3 = FormatHtml.FormatHtmlCode(htmlForm, "<input type=hidden name=str3 value=\"(?<key>.*?)\">");
            string str4 = FormatHtml.FormatHtmlCode(htmlForm, "<input type=hidden name=str4 value=\"(?<key>.*?)\">");
            string bu = FormatHtml.FormatHtmlCode(htmlForm, "<input type=hidden name=bu value=\"(?<key>.*?)\" id=bu>");
            // 发帖标题和内容
            // 将文本转换成 URL 编码字符串
            title = System.Web.HttpUtility.UrlEncode(title, Encoding.GetEncoding("GB2312"));
            content = System.Web.HttpUtility.UrlEncode(content, Encoding.GetEncoding("GB2312"));

            // 要提交的字符串数据。
            formatString =
                     "ct={0}&tn={1}&word={2}&lm={3}&z={4}&sc={5}&cm={6}&bs={7}&str2={8}&str3={9}&str4={10}&bu={11}&ti={12}&co={13}&str1=http%3A%2F%2F&ch1=on&Submit3=%B7%A2%B1%ED%CC%F9%D7%D3";
            postString =
                     string.Format(formatString, ct, tn, word, lm, z, sc, cm, bs, str2, str3, str4, bu, title, content);

            request = WebRequest.Create("http://tieba.baidu.com/f") as HttpWebRequest;
            request.Method = "POST";
            request.Referer = URI;
            request.ContentType = "application/x-www-form-urlencoded";
            request.Accept = "application/x-shockwave-flash, image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, application/vnd.ms-excel, application/vnd.ms-powerpoint, application/msword, */*";
            request.UserAgent = "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1;  Embedded Web Browser from: http://bsalsa.com/; .NET CLR 2.0.50727; CIBA)";
            request.KeepAlive = true;
            request.CookieContainer = cookieContainer;
            // 将提交的字符串数据转换成字节数组
            postData = Encoding.ASCII.GetBytes(postString);
            request.ContentLength = postData.Length;
            // 提交请求数据
            outputStream = request.GetRequestStream();
            outputStream.Write(postData, 0, postData.Length);
            outputStream.Close();

            // 接收返回的页面
            response = request.GetResponse() as HttpWebResponse;
            responseStream = response.GetResponseStream();
            reader = new System.IO.StreamReader(responseStream, Encoding.GetEncoding("GB2312"));
            srcString = reader.ReadToEnd();
            if (srcString.IndexOf("操作成功") > 1)
                sendState = "发送成功!\r\n";
            else
                sendState = "发送失败\r\n";

        }
        

    }
}

            string loginState = "";
            string sendState = "";
            SendtoBaiduTieba.fatie("用户名", "密码","这本书在哪儿看啊","不知道在哪儿看,大家推荐个地放吧","恶魔法则",out loginState,out sendState);

实现了登陆百度贴吧,但是在发帖的时候返回结果为"请不要发广告贴！如您确认所发贴子并非广告贴，请到贴吧投诉吧进行反馈，非常感谢 点击返回 " 哪位大大帮我看看原因出在哪里