The selection quantity & for the selected codes is already being used

What causes this issue?

You are trying to delete codes from a selected set, but these codes are
already being used.
Note that this can lead to problems. It is, for example, no longer
possible to copy the valuation for class characteristic if a deleted
code was used for the valuation.

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?

Check again whether you really need to delete these codes.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.