NBitcoin throws InvalidOperationException with the message Mac HMACSHA256 not recognised

Question

I got the message when I try to sign a transaction:

Transaction payment = new Transaction();
BitcoinSecret PaymentSecret = new BitcoinSecret("1sXCvdpXz...UqkXW9mvT");
...
payment.Sign(Container.PaymentSecret, false);

I dig into the opensource NBitcoin API and figured out these lines give me the error message. What can I do? (https://github.com/NicolasDorier/NBitcoin/blob/master/NBitcoin/Crypto/DeterministicECDSA.cs)

try
{
    hmac = MacUtilities.GetMac(macName);
}
catch(SecurityUtilityException nsae)
{
    throw new InvalidOperationException(nsae.Message, nsae);
}

Answer 1

If someone would like to figure out what is happening exactly, here's a code snippet that'll cause the bug:

    string mechanism = "HMACSHA256";
    if (mechanism.StartsWith("HMAC"))
    {
        Console.WriteLine("good");
    }
    else
    {
        Console.WriteLine("bad");
    }
    Console.ReadLine();