Date & is not a valid working day (calendar &) -> &

What causes this issue?

In <DS:GLOS.factory calendar>factory calendar</> &v2& the date &v1& is
not a valid workday.

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

Please enter a valid (workday ) date (if possible).
<DS:TRAN.SCA3>Display factory calendar &v2&</>

Error message extract from SAP system. Copyright SAP SE.