I am trying to pass a client certificate to a server using the code below however I still revive the HTTP Error 403.7 - Forbidden: SSL client certificate is required. What are the possible reasons the HttpWebRequest would not send the client certificate?

var clientCertificate = new X509Certificate2( @"C:\Development\TestClient.pfx", "bob" );

                    HttpWebRequest tRequest = ( HttpWebRequest )WebRequest.Create( "https://ofxtest.com/ofxr.dll" );

                    tRequest.ClientCertificates.Add( clientCertificate );
                    tRequest.PreAuthenticate = true;
                    tRequest.KeepAlive = true;
                    tRequest.Credentials = CredentialCache.DefaultCredentials;
                    tRequest.Method = "POST";
                    var encoder = new ASCIIEncoding();
                    var requestData = encoder.GetBytes( "<OFX></OFX>" );

                    tRequest.GetRequestStream().Write( requestData, 0, requestData.Length );
                    tRequest.GetRequestStream().Close();

                    ServicePointManager.ServerCertificateValidationCallback = new System.Net.Security.RemoteCertificateValidationCallback( CertPolicy.ValidateServerCertificate );
                    WriteResponse( tRequest.GetResponse() );