Transfer Ownership of GoogleDrive Folder including Subfolders and Files

Question

due to some File migration from a Fileserver to Google Drive for a bunch of users in a company, it is necessary that I change the ownership of a Folder and all its containing subfolders and Files. First I copy the whole folder to my drive(get the ownership this way), then I start my script to transfer the ownership to the new owner.

I wrote a small Script that is working fine for some smaller Folders (<1GB approx.) but almost always gives me an Error when transferring ownership of bigger ones:

Action not allowed (Line 85, File"Code")

Line 85 is containing the following code:

file.setOwner(newOwner);

I have to run that script a few times, sooner or later it finishes successfully.

Have no clue why the script gets that error.

Any Ideas? Many thanks!

The script:

function onOpen() {
  var ui = SpreadsheetApp.getUi();
  ui.createMenu('Transfer')
      .addItem('Transfer Folder', 'Transferfolder')
      .addSeparator()
      .addItem('Disable Sharing Settings for Editors', 'Ownersettings')
      .addToUi();
}


function Transferfolder()
{
  var me=Session.getActiveUser().getEmail();
  var ss = SpreadsheetApp.getActive();
  var data = ss.getDataRange().getValues();
  var idname=data[2][1];  
  var newOwner=data[3][1];
  var fol = DriveApp.getFolderById(idname); 
   subfolderTransfer(fol,me,newOwner);
}
function Ownersettings()
{
  var me=Session.getActiveUser().getEmail();


  var ss = SpreadsheetApp.getActive();
  var data = ss.getDataRange().getValues();
  var idname=data[2][1];  
  var fol = DriveApp.getFolderById(idname);

  disablesharebyeditors(fol,me);
}
function disablesharebyeditors(fol,me)
{

  var files = fol.getFiles();
  var folders=fol.getFolders();


   Logger.log(fol.getOwner().getEmail());
  if(fol.getOwner().getEmail()==me){
  fol.setShareableByEditors(false);
  Logger.log(fol);
  }


  while (files.hasNext())
  {
    var file = files.next();

    if(file.getOwner().getEmail()==me){
    file.setShareableByEditors(false);
    }
  }
  while (folders.hasNext())
  {

    var subfolder = folders.next();

    disablesharebyeditors(subfolder,me);
  }
}

function subfolderTransfer(fol,me,newOwner)
{
 Logger.log("subfolderTransfer");
  var files = fol.searchFiles('"me" in owners');
  var folders=fol.searchFolders('"me" in owners')


  Logger.log(fol.getName());


  if(fol.getOwner().getEmail()==me){
  fol.setOwner(newOwner);

  }
   //file.removeEditor(me);

  while (files.hasNext())
  {
    var file = files.next();
     Logger.log(file.getName());
   if(file.getOwner().getEmail()==me){
    file.setOwner(newOwner);
   }
  }
 Logger.log("folders");
  while (folders.hasNext())
  {Logger.log(fol.getName());

    var subfolder = folders.next();

    subfolderTransfer(subfolder,me,newOwner);
  }
}


function transferfiles(files,me,newOwner)
{

  while (files.hasNext())
  {
    var file = files.next();

    if(file.getOwner().getEmail()==me){
    file.setOwner(newOwner);
    }
    //file.removeEditor(me);
  }
}