X509Certificate2 - the system cannot find the path specified

Möchte ich die Daten von Google analytics über service-Konto.
Wenn ich starten ersten Zeit der Anwendung, funktioniert alles einwandfrei und ich habe Zugriff auf die Daten. Aber Wenn ich starte zweite Zeit der Anwendung habe ich die folgende Fehlermeldung erscheint: "the system cannot find the path specified ". Haben Sie eine Idee? Ich dachte, es kann eine Sperre.

Dies ist mein Quellcode:

   public static String GetAccessToken(string clientIdEMail, string keyFilePath, String scope)
    {
        //certificate
        var certificate = new X509Certificate2(keyFilePath, "notasecret", X509KeyStorageFlags.MachineKeySet | X509KeyStorageFlags.Exportable);

        //header
        var header = new { typ = "JWT", alg = "RS256" };

        //claimset
        var times = GetExpiryAndIssueDate();
        var claimset = new
        {
            iss = clientIdEMail,
            scope = scope,
            aud = "https://accounts.google.com/o/oauth2/token",
            iat = times[0],
            exp = times[1],
        };

        JavaScriptSerializer ser = new JavaScriptSerializer();

        //encoded header
        var headerSerialized = ser.Serialize(header);
        var headerBytes = Encoding.UTF8.GetBytes(headerSerialized);
        var headerEncoded = Convert.ToBase64String(headerBytes);

        //encoded claimset
        var claimsetSerialized = ser.Serialize(claimset);
        var claimsetBytes = Encoding.UTF8.GetBytes(claimsetSerialized);
        var claimsetEncoded = Convert.ToBase64String(claimsetBytes);

        //input
        var input = headerEncoded + "." + claimsetEncoded;
        var inputBytes = Encoding.UTF8.GetBytes(input);

        //signiture
        var rsa = certificate.PrivateKey as RSACryptoServiceProvider;
        var cspParam = new CspParameters
        {
            KeyContainerName = rsa.CspKeyContainerInfo.KeyContainerName,
            KeyNumber = rsa.CspKeyContainerInfo.KeyNumber == KeyNumber.Exchange ? 1 : 2,
            Flags = CspProviderFlags.UseMachineKeyStore
        };
        var aescsp = new RSACryptoServiceProvider(1024,cspParam) { PersistKeyInCsp = false };
        var signatureBytes = aescsp.SignData(inputBytes, "SHA256");
        var signatureEncoded = Convert.ToBase64String(signatureBytes);

        //jwt
        var jwt = headerEncoded + "." + claimsetEncoded + "." + signatureEncoded;

        var client = new WebClient();
        client.Encoding = Encoding.UTF8;
        var uri = "https://accounts.google.com/o/oauth2/token";
        var content = new NameValueCollection();

        content["assertion"] = jwt;
        content["grant_type"] = "urn:ietf:params:oauth:grant-type:jwt-bearer";

        string response = Encoding.UTF8.GetString(client.UploadValues(uri, "POST", content));

        JsonGoogleResponse result = (ser.Deserialize<JsonGoogleResponse>(response));



        return result.access_token;
    }

- Und dies ist der Stapel:

  à   System.Security.Cryptography.CryptographicException.ThrowCryptogaphicException(Int32 hr)
  à System.Security.Cryptography.SafeProvHandle._FreeCSP(IntPtr pProvCtx)
  à System.Security.Cryptography.SafeProvHandle.ReleaseHandle()
  à System.Runtime.InteropServices.SafeHandle.InternalFinalize()
  à System.Runtime.InteropServices.SafeHandle.Dispose(Boolean disposing)
  à System.Runtime.InteropServices.SafeHandle.Finalize()