private void BtnInitialise_Click(object sender, RoutedEventArgs e)
        {
            reader = new CardReader();
            string[] result = reader.PopulateReaders();

            if (result == null)
            {
                MessageBox.Show("Cannot connect to any readers", "Error");
                return;
            }

            LbxReaders.ItemsSource = result;
            LbxReaders.IsEnabled   = IsEnabled;
        }