Ledger & is not a user-defined ledger (long text)

What causes this issue?

The ledger &V1& is a 'standard ledger' or it does not belong to the
application FI-SL ('Special Purpose Ledger', 'Extended General
Ledger'). This program does not currently carry out Customizing
validations for these ledgers.

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 your entry.

Error message extract from SAP system. Copyright SAP SE.