The most common cause is that the Access TaskCentre Schedule Agent service has stopped. This can happen after a server reboot or crash. Restart the service to resume scheduled task execution:
Log in to the server where TaskCentre is installed.
Open Control Panel, then open Administrative Tools.
Double-click Services.
Find the service called 'Access TaskCentre Schedule Agent'.
Right-click the service and select 'Start'. If Start is greyed out, select 'Restart' instead.