Index entry (object type &1) already exists

What causes this issue?

You want to create an index entry of type <LS>&1</>.
LIME has the following object types:
<LS>L</>: Location
<LS>H</>: Handling unit
<LS>S</>: Stock item
The system determined that the index entry already exists and cannot
therefore be created.

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?

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.