[PaleRider]

Prova ADODB.Stream istället.

function saveXmlToFile(xmlDoc, fileName){
  var adoStream = Server.CreateObject("ADODB.Stream");
  adoStream.Open();
  adoStream.Charset = "UTF-8";
  adoStream.WriteText(xmlDoc.xml);
  adoStream.SaveToFile(Server.MapPath("xml/" + fileName));
  adoStream.Close();
}