Duplicate record - initial ledger group already exists for this record

What causes this issue?

In migration template exist records with same key field combinations but
with different ledger group. One of those records contains an empty
ledger group. Posting to an empty ledger group will already post to all
ledgers automatically. Posting on specific ledger group at same time
will cause duplicate records.

System Response

Records with specific ledger will be skipped in data migration if same
records with empty ledger group are also provided via migration
template. Doing this, duplicate records in the same ledger won't be
posted.

How to fix this error?

Check related records in migration template:
If you want to post the record automatically into all ledgers just keep
the record with empty ledger group. Delete the records with specific
ledger group.
If you want to post only into specific ledger, delete the record with
the empty ledger group.

Procedure for System Administrators

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

Error message extract from SAP system. Copyright SAP SE.