What is this warning means?
Warning: Cannot modify header information - headers already sent by (output started at C:\xampp\htdocs\free-prowebsite\site_pro\administrator\adminnav.php:160) in C:\xampp\htdocs\free-prowebsite\site_pro\administrator\admin\file-upload.php on line 224
line 224: header('Location: ' . SUCCESS_URL);