Calculate distance between two Latitude and Longitude value with Google API using C# and VB.Net in ASP.Net

public static double GetDrivingDistanceInMiles(string origin, string destination)
{       
    string url = @"http://maps.googleapis.com/maps/api/distancematrix/xml?origins=" + 
      origin + "&destinations=" + destination + 
      "&mode=driving&sensor=false&language=en-EN&units=imperial";

    HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
    WebResponse response = request.GetResponse();
    Stream dataStream = response.GetResponseStream();
    StreamReader sreader = new StreamReader(dataStream);
    string responsereader = sreader.ReadToEnd();
    response.Close();
    
    XmlDocument xmldoc = new XmlDocument();
    xmldoc.LoadXml(responsereader);


    if (xmldoc.GetElementsByTagName("status")[0].ChildNodes[0].InnerText == "OK")
    {                                            
        XmlNodeList distance = xmldoc.GetElementsByTagName("distance");
        return Convert.ToDouble(distance[0].ChildNodes[1].InnerText.Replace(" mi", ""));
    }

    return 0;
}

xmldoc.LoadXml(responsereader); I have error in this line "Data index at root value is invalid.Line1.Position.1"