sending xml file to webservice

I am posting XML file to Web services using C# .
My work is generating a xml file from object of my application then I should send it on the business Gateway of Monster.com .
I tried this method for sending but I encountred an error "The remote server returned an error: (403) Forbidden."
Please Help !


public void sendFileToWebservice(string file)
        {
            string xmlString = System.IO.File.ReadAllText("C:/Users/DELL/Documents/Visual Studio 2012/Projects/testXML/testXML/file.xml");
            string url = "https://gateway.monster.com:8443/bgwBroker";
            HttpWebRequest req = (HttpWebRequest)WebRequest.Create(url);


            byte[] requestBytes = System.Text.Encoding.ASCII.GetBytes(xmlString);
            req.Method = "POST";
            req.ContentType = "text/xml;charset=utf-8";
            req.ContentLength = requestBytes.Length;
            Stream requestStream = req.GetRequestStream();
            requestStream.Write(requestBytes, 0, requestBytes.Length);
            requestStream.Close();


            HttpWebResponse res = (HttpWebResponse)req.GetResponse();
            StreamReader sr = new StreamReader(res.GetResponseStream(), System.Text.Encoding.Default);
            string backstr = sr.ReadToEnd();
            sr.Close();
            res.Close();
}