微信扫码支付 退款 证书报错系统找不到指定的文件

//是否使用证书
if (isUseCert)
{
string path = HttpContext.Current.Request.PhysicalApplicationPath;

                ServicePointManager.ServerCertificateValidationCallback = new RemoteCertificateValidationCallback(CheckValidationResult);

** X509Certificate cer = new X509Certificate(path + Config.SSLCERT_PATH, SSLCERT_PASSWORD);**

                HttpWebRequest webrequest = (HttpWebRequest)HttpWebRequest.Create(url);
                webrequest.ClientCertificates.Add(cer);
                webrequest.Method = "post";
                HttpWebResponse webreponse = (HttpWebResponse)webrequest.GetResponse();
                Stream stream = webreponse.GetResponseStream();

            }