U3DXT - Cann't post to Facebook

     This is my code:
     public void PostOnFaceBook()
 {
     Application.CaptureScreenshot("Test.png");
     UIImage tmp = new UIImage(Application.persistentDataPath + "/Test.png");
     // share
     if (CoreXT.IsDevice) 
     {
         SocialXT.Post (SLRequest.SLServiceTypeFacebook, _stringPostOnWtitterAndFaceBook, tmp, _link, true);
     }
     System.IO.File.Delete(Application.persistentDataPath + "/Test.png");
 }

if I change text when show popup, post complete to Facebook and show on my timeline. else if I don't change text when show popup and text on popup(that "Test facebook") is default i can't post to facebook.

Please support!