HttpWebRequest _request = (HttpWebRequest)HttpWebRequest.Create(webRequestArgs.Url);

_request.Method = webRequestArgs.method;
if (webRequestArgs.proxy != "")
{
    _request.Proxy = new WebProxy(webRequestArgs.proxy, true);
    _request.Proxy.Credentials = new System.Net.NetworkCredential(webRequestArgs.TechAccUserName, webRequestArgs.TechAccUserPass);
}

if (webRequestArgs.contentType != "")
{
    _request.ContentType = webRequestArgs.contentType;
    _request.ContentLength = webRequestArgs.content.Length;
    StreamWriter _streamWriter = new StreamWriter(_request.GetRequestStream());
    _streamWriter.Write(webRequestArgs.content);
    _streamWriter.Close();

}
if (webRequestArgs.headers != null)
    _request.Headers = webRequestArgs.headers;
_request.CookieContainer = webRequestArgs.CookieContainer;
_request.ClientCertificates.Add(new X509Certificate()); //в и-нете советовали вставить, не помогло


if (webRequestArgs.username != "")
    _request.Credentials = new System.Net.NetworkCredential(webRequestArgs.username, webRequestArgs.pass);
HttpWebResponse _response = (HttpWebResponse)_request.GetResponse(); //здесь вываливается ошибка, что логично