Data entry is not possible for measure '&'

What causes this issue?

The following prerequisites have to be met in order to enter values for
a measure within a scorecard:
At least one of the value fields has to be based on a basic measure.
In the design, a planning area has to be selected for manual data entry
in the scorecard containing at least one of the value fields.

System Response

It is not possible to enter data for this measure.

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.