Process instruction not active: Maintenance not possible

What causes this issue?

The selected value or the selected formula result cannot be
maintained as the corresponding process instruction is deactivated.

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?

If you want to maintain the value, first activate the process
instruction.

Error message extract from SAP system. Copyright SAP SE.