Sharepoint - Recuperar listas en Sharepoint y búscar un elmento en ellas

        listService.Lists listados = new listService.Lists();

        listados.Credentials = new NetworkCredential("xxx", "xxx", "xxx");

        ServicePointManager.ServerCertificateValidationCallback = new System.Net.Security.RemoteCertificateValidationCallback(AcceptAllCertifications);

        XmlDocument xmlDoc = new System.Xml.XmlDocument();
        XmlNode ndQuery = xmlDoc.CreateNode(XmlNodeType.Element, "Query", "");
        XmlNode ndViewFields = xmlDoc.CreateNode(XmlNodeType.Element, "ViewFields", "");
        XmlNode ndQueryOptions = xmlDoc.CreateNode(XmlNodeType.Element, "QueryOptions", "");

        ndViewFields.InnerXml = "";
        if (subruta.Equals(string.Empty))
            ndQueryOptions.InnerXml = "FALSE" + "TRUE" + "" + nombreLista + "/" + ruta + "";
        else
            ndQueryOptions.InnerXml = "FALSE" + "TRUE" + "" + nombreLista + "/" + ruta + subruta + "/" + "";

        listados.Url = urlSharepoint + "/" + nombreSite + "/_vti_bin/Lists.asmx";

        xml = listados.GetListItems(nombreLista, nombreVista, null, ndViewFields, "0", ndQueryOptions, "");


        System.IO.StringReader sr = new System.IO.StringReader(xml.InnerXml);
        XmlTextReader tr = new XmlTextReader(sr);
        DataSet ds = new DataSet("resultDataSet");

        ds.ReadXml(tr);
        if (ds != null && ds.Tables.Count >= 2 && ds.Tables[1].Rows.Count >= 1)
        {
            //Si no existe la columna de LinkFileName la creo a partir de la columna de FileRef
            if (!ds.Tables[1].Columns.Contains("ows_LinkFilename"))
            {
                ds.Tables[1].Columns.Add(new DataColumn("ows_LinkFilename"));
                foreach (DataRow row in ds.Tables[1].Rows)
                {