Duplicate entry in table BSAD_BCK: &1 message(s)

What causes this issue?

There are line items in table BSEG with duplicate entry in the index
table BSAD_BCK.

System Response

The system informs about this inconsistency which has to be corrected in
your productive system before starting the data migration.

How to fix this error?

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

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.