HttpWebRequest - Retrieve NFe

I am accessing the link from the Fazenda website ( link ) in order to return the filled NFe.

When I make the first request I get the Captcha but when I send the Captcha answer it always returns the error "The session has expired. Please consult again.".

I have tried to put Cookie as static but it did not work well ...

The CNPJ query that looks good works with NFe not!

Note: I can not use the WebService because of the date range limitation.

Here is the code for my Query methods:

    public String Consulta(String aNFE, String aCaptcha)
    {
        _hasError = false;
        _msgError = String.Empty;
        String retorno = String.Empty;

        var request = (HttpWebRequest)WebRequest.Create(urlBaseReceitaFederal + paginaValidacao);
        request.ProtocolVersion = HttpVersion.Version10;
        request.CookieContainer = _cookies;
        request.Method = "POST";
        request.Timeout = 10000;
        request.AllowAutoRedirect = true;
        request.UserAgent = "Mozilla/4.0+(compatible;+MSIE+5.01;+Windows+NT+5.0";

        String viewState = PreencherVariavel("<input type=\"hidden\" name=\"__VIEWSTATE\" id=\"__VIEWSTATE\" value=\"", "\" /></div>");
        String eventValidate = PreencherVariavel("<input type=\"hidden\" name=\"__EVENTVALIDATION\" id=\"__EVENTVALIDATION\" value=\"", "\" /></div>            <script");
        String Token = PreencherVariavel("<input type=\"hidden\" name=\"ctl00$ContentPlaceHolder1$token\" id=\"ctl00_ContentPlaceHolder1_token\" value=\"", "\" />             <input type=\"hidden\" name=\"ctl00$ContentPlaceHolder1$captchaSom\"");
        String CaptchaSom = PreencherVariavel("<input type=\"hidden\" name=\"ctl00$ContentPlaceHolder1$captchaSom\" id=\"ctl00_ContentPlaceHolder1_captchaSom\" value=\"", "\" />            <br />            <a id=\"ctl00_ContentPlaceHolder1_hlkAlterarCaptcha\"");
        String viewStateGenerator = PreencherVariavel("<input type=\"hidden\" name=\"__VIEWSTATEGENERATOR\" id=\"__VIEWSTATEGENERATOR\" value=\"", "\" />   <input type=\"hidden\" name=\"__EVENTVALIDATION");

        String postData = "";
        postData = postData + "__EVENTTARGET=&";
        postData = postData + "__EVENTARGUMENT=&";
        postData = postData + "__VIEWSTATE=" + viewState + "&";
        postData = postData + "__VIEWSTATEGENERATOR=" + viewStateGenerator + "&";
        postData = postData + "__EVENTVALIDATION=" + eventValidate + "&";
        postData = postData + "ctl00$ContentPlaceHolder1$PalavraChave=&";
        postData = postData + "ctl00$ContentPlaceHolder1$txtChaveAcessoCompleta=" + aNFE + "&";
        postData = postData + "ctl00$ContentPlaceHolder1$txtCaptcha=" + aCaptcha + "&";
        postData = postData + "ctl00$ContentPlaceHolder1$btnConsultar=Continuar&";
        postData = postData + "ctl00$ContentPlaceHolder1$token=" + Token + "&";
        postData = postData + "ctl00$ContentPlaceHolder1$captchaSom=" + CaptchaSom + "&";
        postData = postData + "hiddenInputToUpdateATBuffer_CommonToolkitScripts=1";

        byte[] byteArray = Encoding.UTF8.GetBytes(postData);
        request.ContentType = "application/x-www-form-urlencoded";
        request.ContentLength = byteArray.Length;

        Stream dataStream = request.GetRequestStream();
        dataStream.Write(byteArray, 0, byteArray.Length);
        dataStream.Close();

        try
        {
            WebResponse response = request.GetResponse();
            StreamReader stHtml = new StreamReader(response.GetResponseStream(), Encoding.GetEncoding("ISO-8859-1"));
            retorno = stHtml.ReadToEnd();
        }
        catch (Exception ex)
        {
            _hasError = true;
            _msgError = ex.Message;

        }

        return retorno;
    }

Att. PHMV