CRYPT_E_UNEXPECTED_MSG_TYPE when creating certificate using certenroll

I am trying to create a self signed cert using certenroll, but I appear to be getting something wrong with the CSignerCertificate::Initialize as it throws an error 0x8009200a CRYPT_E_UNEXPECTED_MSG_TYPE.

'MyCustomRoot' is the name of my self signed root certificate that is in the Current USer->Personal->Certificates store.

        public static X509Certificate2 CertOpen(string subjectName)
    {
        try
        {
            X509Store store = new X509Store("My", StoreLocation.CurrentUser);
            store.Open(OpenFlags.ReadOnly);
            try
            {
                var cer = store.Certificates.Find(
                    X509FindType.FindBySubjectName,
                    subjectName,
                    false);

                if (cer.Count > 0)
                {
                    return cer[0];
                }
                else
                {
                    return null;
                }
            }
            finally
            {
                store.Close();
            }
        }
        catch
        {
            return null;
        }
    }

    public static X509Certificate2 CertCreateNew(string subjectName)
    {
        // create DN for subject and issuer
        var dn = new CX500DistinguishedName();
        dn.Encode("CN=" + subjectName, X500NameFlags.XCN_CERT_NAME_STR_NONE);


        // create a new private key for the certificate
        CX509PrivateKey privateKey = new CX509PrivateKey();
        privateKey.ProviderName = "Microsoft Base Cryptographic Provider v1.0";
        privateKey.MachineContext = false;
        privateKey.Length = 2048;
        privateKey.KeySpec = X509KeySpec.XCN_AT_SIGNATURE; // use is not limited
        privateKey.ExportPolicy = X509PrivateKeyExportFlags.XCN_NCRYPT_ALLOW_PLAINTEXT_EXPORT_FLAG;
        privateKey.Create();


        var hashobj = new CObjectId();
        hashobj.InitializeFromAlgorithmName(ObjectIdGroupId.XCN_CRYPT_HASH_ALG_OID_GROUP_ID,
            ObjectIdPublicKeyFlags.XCN_CRYPT_OID_INFO_PUBKEY_ANY,
            AlgorithmFlags.AlgorithmFlagsNone, "SHA256");

        // add extended key usage if you want - look at MSDN for a list of possible OIDs
        var oid = new CObjectId();
        oid.InitializeFromValue("1.3.6.1.5.5.7.3.1"); // SSL server
        var oidlist = new CObjectIds();
        oidlist.Add(oid);
        var eku = new CX509ExtensionEnhancedKeyUsage();
        eku.InitializeEncode(oidlist);




        // Create the self signing request
        var cert = new CX509CertificateRequestCertificate();

        X509Certificate2 signer = CertOpen("MyCustomRoot");
        if (signer == null)
        {
            throw new CryptographicException("Signer not found");
        }
        Console.WriteLine(signer.Subject);
        String base64str = Convert.ToBase64String(signer.RawData);


        ISignerCertificate signerCertificate = new CSignerCertificate();
        signerCertificate.Initialize(false, X509PrivateKeyVerify.VerifySilent, EncodingType.XCN_CRYPT_STRING_BASE64, base64str);
        cert.InitializeFromPrivateKey(X509CertificateEnrollmentContext.ContextUser, privateKey, "");
        cert.Subject = dn;
        cert.Issuer.Encode(signer.Subject, X500NameFlags.XCN_CERT_NAME_STR_NONE);
        cert.NotBefore = DateTime.Now; //start date
        cert.NotAfter = DateTime.Now.AddYears(10); // expires date
        cert.X509Extensions.Add((CX509Extension)eku); // add the EKU
        cert.HashAlgorithm = hashobj; // Specify the hashing algorithm
        cert.Encode(); // encode the certificate

        // this line MUST be called AFTER IX509CertificateRequestCertificate.InitializeFromPrivateKey call,
        // otherwise you will get OLE_E_BLANK uninitialized object error.

        cert.SignerCertificate = (CSignerCertificate)signerCertificate;






        // Do the final enrollment process
        var enroll = new CX509Enrollment();
        enroll.InitializeFromRequest(cert); // load the certificate
        enroll.CertificateFriendlyName = subjectName; // Optional: add a friendly name

        string csr = enroll.CreateRequest(); // Output the request in base64
                                             // and install it back as the response
        enroll.InstallResponse(InstallResponseRestrictionFlags.AllowUntrustedCertificate,
            csr, EncodingType.XCN_CRYPT_STRING_BASE64, ""); // no password
                                                            // output a base64 encoded PKCS#12 so we can import it back to the .Net security classes
        var base64encoded = enroll.CreatePFX("", // no password, this is for internal consumption
            PFXExportOptions.PFXExportChainWithRoot);

        // instantiate the target class with the PKCS#12 data (and the empty password)
        return new System.Security.Cryptography.X509Certificates.X509Certificate2(
            System.Convert.FromBase64String(base64encoded), "",
            // mark the private key as exportable (this is usually what you want to do)
            System.Security.Cryptography.X509Certificates.X509KeyStorageFlags.Exportable
        );
    }

Where am I going wrong?

I reproed the code and it seems that signer certificate referenced in ISignerCertificate object returned from CertOpen method doesn't have a private key.

To ensure this, try to add this condition in CertOpen method:

if (cer.Count > 0 && cer[0].HasPrivateKey)
{
    return cer[0];
}