XML : Attempting to save to an existing xml file

I am trying to update some values onto my xml file. It is constantly nagging me about an operation that is not permitted on IsolatedStorageFileStream. Here is my code:

  using (var storage = IsolatedStorageFile.GetUserStoreForApplication())          {              using (Stream stream = storage.OpenFile("ListsSavedFiles.xml", FileMode.Open))              {                  XDocument storedLists = XDocument.Load(stream);                  var newList = new XElement("list",                                new XElement("code", code.ToString().ToLower()),                                new XElement("name", lists_AddList_NameField.Text.ToString()),                                new XElement("date", DateTime.Now.Date.ToString()));                    storedLists.Element("lists").Add(newList);                  storedLists.Save(stream);                    var lists = (from query in storedLists.Descendants("list")                               select new ListsXmlListBinder                               {                                   ListName = query.Element("name").Value,                                   ListDate = query.Element("date").Value                               }).ToList();                    lists_ListViewer.ItemsSource = lists;              }          }    

Anyway this issue can be resolved? Thanks!