Period warnings occur when a parent task can not be recalculated due to a constrain, such as a blocking task (for example a task in Locked mode), non-working day, or when you use the manual period mode. 

The warning is displayed as a yellow box with a dashed-line frame and shows the position of the parent tasks calculated based on its children.

Showing Period Warnings

The warning can only be displayed using the Gantt module. To show the warnings, click on View > Period warnings.

Rescheduling Tasks Manually

Parent tasks in manual mode can be manually rescheduled so the task period is calculated based on children tasks. To reschedule the task manually, click on the task to show the tasks' details and click Reschedule:

Bulk Rescheduling

To fix all the warnings, switch to one of the Auto period modes.