This error is probably related to a byte order mark (BOM) prior to the actual XML content. You need to parse the returned String and discard the BOM, so SAXParser can process the document correctly. You will find a possible solution here.
I normally use another way to do the same using System.Xml; using System.Net; using System.IO; public static void CallWebService() { var _url = “http://xxxxxxxxx/Service1.asmx”; var _action = “http://xxxxxxxx/Service1.asmx?op=HelloWorld”; XmlDocument soapEnvelopeXml = CreateSoapEnvelope(); HttpWebRequest webRequest = CreateWebRequest(_url, _action); InsertSoapEnvelopeIntoWebRequest(soapEnvelopeXml, webRequest); // begin async call to web request. IAsyncResult asyncResult = webRequest.BeginGetResponse(null, null); // suspend this thread … Read more