& inactive default set will be saved and must be activated before use

What causes this issue?

You have maintained default sets and saved the data. However, one set
has not been activated . This is indicated by a yellow light. Active
default sets are shown with a green light. Faulty default sets are shown
with a red light. Sets are faulty if the activation has failed once
before. This may be caused by incorrect parameters.
If you save the inactive default set, the system will not use this set
for the conversion process.

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

System Response

The system saves all entered sets to the database.

How to fix this error?

If you want inactive sets to be used, go back to this transaction and
activate the sets by choosing <ZK>Active single set</> or <ZK>Activate
w/o check</> or <ZK>Mass Activation</>. Note that if you choose
<ZK>Activate w/o check</>, incorrect sets may be saved which lead to
quantity conversion errors when goods movements are posted.

Error message extract from SAP system. Copyright SAP SE.