WCF sevice Error when accessing from application

This is my code...

HttpWebRequest req = null;
HttpWebResponse res = null;
try
{
const string url = "http://localhost:4567/PersonServiceImpl.svc/auth";
req = (HttpWebRequest) WebRequest.Create(url);
req.Method = "POST";
req.ContentType = "application/xml; charset=utf-8";
req.Timeout = 30000;
req.Headers.Add("SOAPAction", url);

var xmlDoc = new XmlDocument {XmlResolver = null};
xmlDoc.Load(Server.MapPath("PostData.xml"));
string sXml = xmlDoc.InnerXml;
req.ContentLength = sXml.Length;
var sw = new StreamWriter(req.GetRequestStream());
sw.Write(sXml);
sw.Close();

res = (HttpWebResponse) req.GetResponse(); //I got Error here
Stream responseStream = res.GetResponseStream();
var streamReader = new StreamReader(responseStream);

//Read the response into an xml document
var soapResonseXmlDocument = new XmlDocument();
soapResonseXmlDocument.LoadXml(streamReader.ReadToEnd());

//return only the xml representing the response details (inner request)
TextBox1.Text = soapResonseXmlDocument.InnerXml;
//Response.Write(soapResonseXMLDocument.InnerXml);
}
catch (Exception ex)
{
Response.Write(ex.Message);
}