Master inspection characteristic is already linked to class char. &1

What causes this issue?

You have edited a version of this master inspection characteristic and
linked it to a class characteristic. However, one of the existing
verisons of the master inspection characteristic is already linked to a
different class characteristic. This is not allowed.

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?

Delete the class characteristic from the version you have just edited
or enter the class characteristic that has already been assigned in the
different version.

Error message extract from SAP system. Copyright SAP SE.