Storage location already exists; correct your entry or it will be ignored

What causes this issue?

While entering storage locations collectively, you have entered a
storage location that already exists.

How to fix this error?

INCLUDE NA_EINGABE_PRUEFEN
If you have made a typing error, correct your entry.
If you do not correct your entry, it will be ignored by the system.

Error message extract from SAP system. Copyright SAP SE.