when call web service at that time given issuse

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C#

WCFServices

i am calling my web service for this format my request parameter with soap format like this

<s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/">
  <s:Header>
    <Action s:mustUnderstand="1" xmlns="http://schemas.microsoft.com/ws/2005/05/addressing/none">http://tempuri.org/IMessageContract/GetAuthorInfo</Action>
    <h:AuthorIdentity xmlns:h="http://tempuri.org/">db2972</h:AuthorIdentity>
  </s:Header>
  <s:Body>
    <AuthorRequest xmlns="http://tempuri.org/" />
  </s:Body>
</s:Envelope>

and i am calling this web service for code behind so give me the error like this
The remote server returned an error: (400) Bad Request.

So please give me the suggestion for this

string resultXml;
          const string url = "http://localhost:50399/MessageContract.svc";
          WebRequest wbrqst = WebRequest.Create(url);
          HttpWebRequest httpreq = (HttpWebRequest)wbrqst;
          httpreq.Method = "POST";
          httpreq.ContentType = "text/xml";
          httpreq.Headers.Add("SOAPAction", url);
          httpreq.ProtocolVersion = HttpVersion.Version11;
          httpreq.Credentials = CredentialCache.DefaultCredentials;
          Stream requestStream = httpreq.GetRequestStream();
          StreamWriter streamWriter = new StreamWriter(requestStream, Encoding.ASCII);
          StringBuilder sb = new StringBuilder();
          sb.Append("<s:Envelope xmlns:s=\"http://schemas.xmlsoap.org/soap/envelope/\">");
          sb.Append("<s:Header>");
          sb.Append("<Action s:mustUnderstand=\"1\" xmlns=\"http://schemas.microsoft.com/ws/2005/05/addressing/none\">http://tempuri.org/IMessageContract/GetAuthorInfo</Action>");
          sb.Append("<h:AuthorIdentity xmlns:h=\"http://tempuri.org/\">db2972</h:AuthorIdentity>");
          sb.Append("</s:Header>");
          sb.Append("<s:Body>");
          sb.Append("<AuthorRequest xmlns=\"http://tempuri.org/\" />");
          sb.Append("</s:Body>");
          sb.Append("</s:Envelope>");
          streamWriter.Write(sb.ToString());
          streamWriter.Close();

          HttpWebResponse wr = (HttpWebResponse)httpreq.GetResponse();
          StreamReader srd = new StreamReader(wr.GetResponseStream());
          resultXml = srd.ReadToEnd();