Library default set & does not exist

What causes this issue?

The library default set you have entered has not been defined yet.

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 the set ID and select an existing set. If you do not know any
valid set IDs, press F4 to display possible entries.

Error message extract from SAP system. Copyright SAP SE.