Why wouldn't an app recognize a Certificate with a CSP of "Microsoft Software Key Storage Provider"...

Question

...but will recognize the same Cert with the CSP set to "Microsoft Enhanced RSA and AES Cryptographic Provider"?

In other words, the app fails when I import the certificate into the server's local key store like this:

certutil.exe -importpfx <certificate file path>\<certificate file>

but works if I override the CSP like this:

certutil.exe -csp "Microsoft Enhanced RSA and AES Cryptographic Provider" -importpfx <certificate file path>\<certificate file>

Here is the relevant section of code:

var store2 = X509CertificateStore.LocalMachineStore(X509CertificateStore.MyStore);
store2.OpenRead();

var coll2 = store2.FindCertificateBySubjectString(ConfigurationManager.AppSettings["<redacted>"]);

if (coll2.Count > 0) {
  var cert2 = coll2[0];
  var certType = cert2.GetType();
  var cert3 = new X509Certificate2(cert2);
  certType = cert3.GetType();
  if (cert2.SupportsDigitalSignature) {
    svc.ClientCredentials.ClientCertificate.Certificate = new X509Certificate2(cert2);
    }
  } 
else throw new Exception("Certificate attachment failed.");

var currentUser = SessionHelper.CurrentUser;
var svcAddress = Settings.Default.App_Service_WebService;

results = svc.getresultsByPersonIdentifier(PersonIdentifier.Text, identifier.PI, out responseCd, out responseMsg);

The code throws an Invalid Service Provider when it invokes the web service at the end of the snippet.