Erro Cs1503

Programação
#1

private static bool VerifyXml(XmlDocument Doc, AsynXmlCrypt.KeyManager Key)
{
if(Doc == null)
throw new ArgumentException(“xmlDoc”);
if (Key == null)
throw new ArgumentException(“key”);

        // Create a new SignedXml object and pass it
        // the XML document class.
        SignedXml signedXml = new SignedXml(Doc);

        // Find the "Signature" node and create a new
        // XmlNodeList object.
        XmlNodeList nodeList = Doc.GetElementsByTagName("Signature");

        // Throw an exception if no signature was found.
        if (nodeList.Count <= 0)
        {
            throw new CryptographicException("Verification failed: No Signature was found in the document.");
        }

        // This example only supports one signature for
        // the entire XML document.  Throw an exception 
        // if more than one signature was found.
        if (nodeList.Count >= 2)
        {
            throw new CryptographicException("Verification failed: More that one signature was found for the document.");
        }

        // Load the first <signature> node.  
        signedXml.LoadXml((XmlElement)nodeList[0]);

        // Check the signature and return the result.
        return signedXml.CheckSignature(Key);

}
Estou trabalhando com assinatura digital e gostaria de checar se assinatura está válida. Porém quando eu retorno ( return
signedXml.CheckSignature(Key);fala que não é possível de converter de AsynXmlCrypt.KeyManager para System.Security.Cryptograpnhy.AsymetricAlgorithm.
E com isso a minha assinatura passa como invalida pois não consigo retorna lá para está função
try
{
Console.WriteLine(“Verifying signature…”);
bool result = VerifyXml(Doc, Key);

            // Display the results of the signature verification to 
            // the console.
            if (result)
            {
                Console.WriteLine("The XML signature is valid.");
            }
            else
            {
                Console.WriteLine("The XML signature is not valid.");
            }
        }
        catch (Exception e)
        {
            Console.WriteLine(e.Message);
        }