Inconsistent characteristic value assignment

You want to change the value assigned to a characteristic. However, the
change causes inconsistency, so the new value is not allowed.
The inconsistency may be for the following reasons:
A precondition or selection condition is violated.
The characteristic is a single-value characteristic, and different
values have been set by constraints, actions, or procedures.
In classification, inconsistencies occur when you change the value set
of a characteristic if objects or classes have already been classified
with values from the previous value set (for example, in the case of a
configurable material or a generic material).

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?

Choose Inconsistencies to see what triggered the inconsistency.
You can also use the explanation facility for more information.
Delete the values that triggered the inconsistency.
You can only change or delete a value or value set that has already been
used to classify objects if you delete the existing allocations.

Error message extract from SAP system. Copyright SAP SE.