货币转换问题一再出现

Question

我有类帮助将usd转换为inr现在正在给出错误，这就是：

  

指定的参数超出了有效值的范围。

在此行代码行中：

var result = Regex.Matches(streamReader.ReadToEnd(), "<span class=\"?bld\"?>([^<]+)</span>")[0].Groups[1]

这是一个完整的课程：

public static decimal CurrencyConvert(decimal amount, string fromCurrency, string toCurrency)
{
     //Grab your values and build your Web Request to the API
     string apiURL = String.Format("http://finance.google.com/finance/converter?a={0}&from={1}&to={2}&meta={3}", amount, fromCurrency, toCurrency, Guid.NewGuid().ToString());
     //Make your Web Request and grab the results
     var request = WebRequest.Create(apiURL);         
     //Get the Response
     var streamReader = new StreamReader(request.GetResponse().GetResponseStream(), Encoding.ASCII);
     //Grab your converted value (ie 2.45 USD)
     var streamData = streamReader.ReadToEnd();
     var result = Regex.Matches(streamData, "<span class=\"?bld\"?>([^<]+)</span>")[0].Groups[1].Value;
     //Get the Result
     return Convert.ToDecimal(result.Replace(" INR", ""));
}