Currency conversion in WPF

void OnClick_Convert(object sender, RoutedEventArgs e)
       {
           try
           {
               double dResult = 0;
               //store the default brush for the convert button before call
               Brush dbrush=this.btnConvert.Background;
               //change the background of convert button before call
               this.btnConvert.Background = Brushes.LightBlue;
               //create the CurrencyConvertor webserivce
               CurrencyConvertorSoapClient wsCurrencyConverter = new CurrencyConvertorSoapClient();
               //call the webmethod
               dResult = wsCurrencyConverter.ConversionRate((Currency)Enum.Parse(typeof(Currency), cmbFromCurrency.SelectionBoxItem.ToString().Substring(0, 3)), (Currency)Enum.Parse(typeof(Currency), cmbToCurrency.SelectionBoxItem.ToString().Substring(0, 3)));
               txtResults.Text = cmbFromCurrency.SelectionBoxItem.ToString() + " To " + cmbToCurrency.SelectionBoxItem.ToString() + " = " + Convert.ToString(dResult);
               //change back the to default brush
               this.btnConvert.Background = dbrush;
           }
           catch (Exception ex)
           {
               MessageBox.Show(ex.Message, "Error", MessageBoxButton.OK);
           }

public double ConversionRate(www.webservicex.net.Currency FromCurrency, www.webservicex.net.Currency ToCurrency)
   {
       return base.Channel.ConversionRate(FromCurrency, ToCurrency);
   }