This error means the TaskCentre server is currently in Maintenance Mode. Restarting the TaskCentre Server Service will resolve this. Follow these steps:
Log in to the server where TaskCentre is installed.
Open Control Panel.
Open Administrative Tools (location may vary by operating system).
Double-click Services.
Find Access TaskCentre Service in the list.
Right-click Access TaskCentre Service and select Start. If Start is greyed out, select Restart.
A loading bar appears while the service restarts and closes automatically when it is running again. 'Running' appears in the status column to confirm success. To prevent this from happening in future, ensure that disallowed time is set for the Maintenance period and the period before it — this prevents tasks from delaying Maintenance.
In TaskCentre, click Tools, then click Options, then click Run Times and Maintenance.