Product group is not allowed in MRP area &1 for MRP set &2

What causes this issue?

Product groups cannot be maintained for MRP area &v1&.
If you work in this client in MRP <ZH>with</>
<DS:GLOS.3526C359AFAB52B9E10000009B38F974>MRP areas</>, product groups
are only permitted on plant level or on the level of the plant MRP
area.

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?

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.