Working hours &1 for factory calendar &2 are invalid

What causes this issue?

The system has found an invalid, or unavailable work time indicator
during delivery and transportation scheduling. The work time is &V1& in
factory calendar &V2&.
The work times and/or factory calendars were probably deleted in
Customizing, even though they would still be referred to.

System Response

Scheduling is terminated, all deadlines are set to the start date of
the scheduling.

How to fix this error?

Ensure that the work times &V1& for factory calendar &V2& are
maintained in table TTSTRSD.

Error message extract from SAP system. Copyright SAP SE.