How to avoid Not on FX application thread; currentThread = JavaFX Application Thread error?

Below code snippets is giving me error Not on FX application thread; currentThread=JavaFX Application Thread.This application was working fine in java 1.7 but when i moved it to fx8 it is now giving error. when I start the application on my 1st attempt it is working as intended .But after closing the stage and opening it again it is not working.

The error is also ambiguous Not On fx application thread and current thread- javafx application thread.What did it mean by not on fx application thread if the current thread is a fx application thread.

progressDialog = createProgressDialog(service);
progressDialog.show();
progressDialog.setOnCloseRequest(new EventHandler<WindowEvent>() {
    @Override
    public void handle(WindowEvent event) {
        // if (service.isRunning()) {
        // service.cancel();
        progressDialog.close();
        // }
    }
});

@SuppressWarnings("unchecked")
private Stage createProgressDialog(final Service<IStatus> service) {
    stage = new Stage();

    URL url = FileLocator.find(Activator.getDefault().getBundle(),
    new Path("icons/xxx_16x16.png"), null); //$NON-NLS-1$
    stage.getIcons().add(new Image(url.getFile()));
    stage.setTitle("Downloading ..."); //$NON-NLS-1$
    // Creating StackPane
    stage.initModality(Modality.WINDOW_MODAL);
}

Solution 1:

Calling

Platform.runLater(new Runnable(){
// do your GUI stuff here
});

will fix it.

Solution 2:

This happened with me when i was modifying UI element from task in javafx 2 like listview elements.A Task Which Modifies The Scene Graph helped me to solve the issue i.e. updating UI elements by

 final ListView<String> group = new ListView ();

 Task<Void> task = new Task<Void>() {

     @Override protected Void call() throws Exception {

         group.getItems().clear();  

          for (int i=0; i<100; i++) {                
             Platform.runLater(new Runnable() {
                 @Override public void run() {
                     group.getItems.add(i);
                 }
             });
         }
         return null;
     }
 };