MessageBodyWriter not found for media type=application/x-hl7

We try to post an XML doc on a web server using the following code and we receive the error message: "org.glassfish.jersey.message.internal.MessageBodyProviderNotFoundException: MessageBodyWriter not found for media type=application/x-hl7". What we do wrong? Any help we be appreciated.

private void postWebClientTypeVisit()
{
   XmlDocument doc = new XmlDocument();
   doc.LoadXml(createStringXML());
   string myParameters = doc.InnerXml;

   string URI = "http://ift.tt/1BBZKL0";

   WebClient wc = new WebClient();
   wc.Headers[HttpRequestHeader.Authorization] = "Bearer " + accessToken;
            wc.Headers[HttpRequestHeader.Accept] = "application/x-hl7";

   string HtmlResult = wc.UploadString(URI, myParameters);
}

...createStringXML() is something like that:

private static string createStringXML()
{
  string str = @"<?xml version='1.0' encoding='UTF-8'?>" +
               @"<ClinicalDocument xmlns='urn:hl7-org:v3' xmlns:xsi='http://ift.tt/ra1lAU' xsi:schemaLocation='urn:hl7-org:v3 CDA.xsd'>" +
               //.....
               @"<title>PRESCRIPTIONS</title><text /></section></component></structuredBody></component></ClinicalDocument>";

  return str;
}