You may meet the following error when trying to run a cron in Drupal
- Attempting to re-run cron while it is already running.
Or the cron was completed immediately after u input the cron.php url in browser.
When you get the above situations, that means your cron fails. To resolve the issue, delete the following to record in your Drupal database.
- delete from variable where name = “cron_last”;
- delete from variable where name = “cron_semaphore”;
Then clear the Drupal cache and your cron should be able to run now.