Scheduler.php cron error

Yesterday I upgraded from Freepbx 2.11 to 12 and since then I’ve been getting the below error when the scheduler.php cron job runs. Does anyone have any idea what the cause might be and how to resolve it?

PHP Fatal error:  Uncaught exception 'Exception' with message 'Severe Error getting 1424487600. This could indicate a database error' in /var/www/htdocs-secure/freepbx/admin/modules/dashboard/classes/PruneHistory.class.php:144
Stack trace:
#0 /var/www/htdocs-secure/freepbx/admin/modules/dashboard/classes/PruneHistory.class.php(125): PruneHistory->calcAverages(Array, 'HOUR')
#1 /var/www/htdocs-secure/freepbx/admin/modules/dashboard/classes/PruneHistory.class.php(113): PruneHistory->commitAvg(Array, 1424476800, 'HOUR')
#2 /var/www/htdocs-secure/freepbx/admin/modules/dashboard/classes/PruneHistory.class.php(59): PruneHistory->avgPeriod('HOUR')
#3 /var/www/htdocs-secure/freepbx/admin/modules/dashboard/Dashboard.class.php(200): PruneHistory->doPrune()
#4 /var/www/htdocs-secure/freepbx/admin/modules/dashboard/Dashboard.class.php(189): Dashboard->pruneSysInfo()
#5 /var/www/htdocs-secure/freepbx/a in /var/www/htdocs-secure/freepbx/admin/modules/dashboard/classes/PruneHistory.class.php on line 144