Account &1 already exists up to &2 in controlling area &3

What causes this issue?

You attempted to create the controlling-area-specific area for a G/L
account. This area already exists, however, albeit with restricted
validity.
This can occur in particular if a cost element has already lost its
validity before the current fiscal year at the time of migration.

System Response

The system prevents you from saving.

How to fix this error?

A controlling-area-specific area for a G/L account with restricted
validity cannot be changed.

Procedure for System Administrators

If this situation was not intentional, refer to SAP Note 2223514.

Error message extract from SAP system. Copyright SAP SE.