This is usually caused by the Magento cron not being executed on your Magento site. Make sure is enabled and running every 5 mins.
To set up your Magento Cron in cPanel visit: https://youtu.be/phGTGS43U-M?t=40
To set up cron using command line: http://devdocs.magento.com/guides/m1x/install/installing_install.html#install-cron
If you're using a custom hosting manager contact your hosting provider or contact us and will be happy to assist you.
 Cron automatically schedules tasks to be executed in the future. Several Magento features require cron to be running in your system.