The entry of a factory calendar is only appropriate with a time duration

What causes this issue?

If you enter a factory calendar ID, you must also specify a duration.

System Response

The system can use a factory calendar for calculating the critical
duration. If you only enter a calendar ID, the system is unable to
determine the critical duration.

How to fix this error?

Enter a critical duration in addition to the factory calendar.

Error message extract from SAP system. Copyright SAP SE.