Locating the location of a visitor visiting My website.

public void GetIP()
{
string Str = "";
Str = System.Net.Dns.GetHostName();
IPHostEntry ipEntry = System.Net.Dns.GetHostEntry(Str);
IPAddress[] addr = ipEntry.AddressList;
//return addr[addr.Length - 2].ToString();
GetLocation(addr[addr.Length - 2].ToString());


}
public DataTable GetLocation(string strIPAddress)
{
//Create a WebRequest with the current Ip
WebRequest _objWebRequest =
WebRequest.Create("http://ws.cdyne.com/ip2geo/ip2geo.asmx/ResolveIP?ipAddress="
+ strIPAddress);
//Create a Web Proxy
WebProxy _objWebProxy =
new WebProxy("http://ws.cdyne.com/ip2geo/ip2geo.asmx/"
+ strIPAddress, true);

//Assign the proxy to the WebRequest
_objWebRequest.Proxy = _objWebProxy;

//Set the timeout in Seconds for the WebRequest
_objWebRequest.Timeout = 2000;

try
{
//Get the WebResponse
WebResponse _objWebResponse = _objWebRequest.GetResponse();//The remote server returned an error: (500) Internal Server Error.
//Read the Response in a XMLTextReader
XmlTextReader _objXmlTextReader
= new XmlTextReader(_objWebResponse.GetResponseStream());

//Create a new DataSet
DataSet _objDataSet = new DataSet();
//Read the Response into the DataSet
_objDataSet.ReadXml(_objXmlTextReader);

return _objDataSet.Tables[0];
}
catch
{
return null;
}
}

i have marked the place where i am getting error.
//The remote server returned an error: (500) Internal Server Error.