Unable to connect to the remote server

req.Timeout=System.Threading.Timeout.Infinite;

public string SendSMS(string_message, string_phone_number)
{
    varenc=System.Text.Encoding.GetEncoding("EUC-JP");
    var postData="";

    try
    {
        // Create a string to POST
        postData=postData+String.Format("username={0}&", HttpUtility.UrlEncode(_username)));
        postData=postData+String.Format("password={0}&", HttpUtility.UrlEncode(_password)));
        postData=postData+String.Format("trigger_id={0}&", HttpUtility.UrlEncode(_trigger_id1));
        postData=postData+String.Format("phone_number={0}&", HttpUtility.UrlEncode(_PhoneNumber));
        postData=postData+String.Format("message={0}&", HttpUtility.UrlEncode(_message)));

        // Replace with byte array
        var postDataBytes=System.Text.Encoding.ASCII.GetBytes(postData);
        // Create WebRequest
        System.Net.WebRequest req = System.Net.WebRequest.Create(_SMSURL);

        req.Timeout = System.Threading.Timeout.Infinite;

        // Specify POST for the method
        req.Method="POST";
        // Set ContentType to "application/x-www-form-urlencoded"
        req.ContentType="application/x-www-form-urlencoded";
        // Specify the length of data to POST
        req.ContentLength=postDataBytes.Length;
        // Get Stream to POST data
        System.IO.Stream reqStream=req.GetRequestStream();

        // Write data to send
        reqStream.Write (postDataBytes, 0, postDataBytes.Length);

        reqStream.Close();

        // Get WebResponse to receive responses from the server
        varres=req.GetResponse();
        // Get Stream to receive response data
        varresStream=res.GetResponseStream();
        // To XML format
        varobjXMLReader=newXmlTextReader(resStream);

        var xmldoc = new XmlDocument();
        xmldoc.Load(objXMLReader);
        objXMLReader.Close();
    }
    catch (Exception e)
    {
        return "Send SMS Error" + e.Message + "log:" +_log;
    }
}