other C# trouble

  public void updateData(string url, string file)
                {
                    if (url == "")
                    {
                        MessageBox.Show("No address specified !");
                    }
                    else
                    {
                        string http = url.Substring(0, 6);
                        if (http != "http://")
                        {
                            http = "http://";
                            url = http + url;
                        }
                        if (!check_link(url, file))
                        {
                            MessageBox.Show("This link " + url + " already exists !");
                        }
                        else
                        {
                            XmlDocument document = new XmlDocument();
                            document.Load(file);
                            XmlElement element = document.CreateElement("link");
                            element.InnerText = url;
                            document.DocumentElement.AppendChild(element);
                            document.PreserveWhitespace = false;
                            XmlTextWriter xtw = new XmlTextWriter(file, Encoding.UTF8);
                            document.WriteTo(xtw);
                            xtw.Close();
                            document.Save(file);
                            showData(file);
                        }
                    }
              }
        public bool check_link(string url,string file)
        {
            bool status = false;
            XmlReaderSettings setari = new XmlReaderSettings { IgnoreWhitespace = true, IgnoreComments = true };
            XmlReader reader = XmlReader.Create(file,setari);
            while(reader.Read())
            {
                switch (reader.NodeType)
                {
                    case XmlNodeType.Element :
                        switch (reader.Name)
                        {
                            case "link": {
                                string own_value = reader.ReadString();
                                if (own_value == url)
                                {
                                    status=false;
                                }
                                else
                                {
                                    status=true;
                                }
                                break; }
                        }
                        break;
                }
            }
            reader.Close();

                return status;
        }