Phrase &1 in characteristic &2 is from passive library

What causes this issue?

This error can occur for the following reasons:
The phrase is contained in a passive library and cannot therefore be
used to assign values to substances manually.
After an import, a phrase from a passive library is assigned as a value
assignment. However, you can only maintain a value assignment manually
if it no longer contains a phrase from a passive library.

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?

Assign a valid phrase from the active library as the value assignment.

Error message extract from SAP system. Copyright SAP SE.