爬网页数据，403错误，但浏览器可以正常打开

            HttpWebRequest httpReq;
            HttpWebResponse httpResp;
            string strHtml = "";
            Uri httpURL = new Uri(Url);
            httpReq = (HttpWebRequest)WebRequest.Create(httpURL);
            httpReq.ProtocolVersion = HttpVersion.Version11;
            try
            {
                httpResp = (HttpWebResponse)httpReq.GetResponse();
                StreamReader reader = new StreamReader(httpResp.GetResponseStream(), Encoding.UTF8);
                strHtml = reader.ReadToEnd();
            }
            catch (WebException exception)
            {
                HttpWebRequest hReq;
                HttpWebResponse hResp;
                if (exception.Status == WebExceptionStatus.ConnectionClosed 
                    && exception.Response == null)
                {
                    hReq = (HttpWebRequest)WebRequest.Create(httpURL);
                    hReq.ProtocolVersion = HttpVersion.Version10;
                    try
                    {
                        //hResp.ProtocolVersion = HttpVersion.Version10;
                        hResp = (HttpWebResponse)hReq.GetResponse();
                    }
                    catch (WebException exception1)
                    {
                        if (exception1.Status == WebExceptionStatus.ProtocolError
                        && exception1.Response != null
                        && exception1.Response is HttpWebResponse)
                        {
                            StreamReader reader = new StreamReader(((HttpWebResponse)exception1.Response).GetResponseStream(), Encoding.UTF8);
                            strHtml = reader.ReadToEnd();
                            lstBoxInfo.Items.Add(((HttpWebResponse)exception1.Response).StatusCode);
                        }
                    }
                }
                else if (exception.Status == WebExceptionStatus.ProtocolError
                        && exception.Response != null
                        && exception.Response is HttpWebResponse)
                {
                    StreamReader reader = new StreamReader(exception.Response.GetResponseStream(), Encoding.UTF8);
                    strHtml = reader.ReadToEnd();
                }

开始查了下用HttpVersion.Version11版本，异常中的respose为空，所以用10版本在异常捕获中，就可以得到。
但现在出现了 一个问题，在异常捕获中获得的reader是被截取的，最大65535，假如数据过大，就不是一个完整的html，丢数据。
求各位高手有什么解决办法，针对403 Forbidden的问题，关键浏览器都可以正常打开，而且查看到html都是正常完整的。