I use $_SERVER['DOCUMENT_ROOT']."/lib/sft_required.php"; to include the 'sft_required' file in a PHP script. When I run this file using browser, it works fine but when I run this as a cron job job, it does not work. It seems that the file is not included when we run the script through cron.
Assuming you are running the script directly through cron (as opposed to from a web server accessed by an HTTP request triggered by a cronjob (e.g. by cron running wget)), then of course it doesn't work.
