Field help (LEDCMM) 

A ledger can manage an account management of type 'Commitments' only if the ledger is analytical.
In the case of a company having several ledgers managing commitments, the latter are generated on all the ledger checked 'Commitments".

SEEINFO Upon generation of commitments/precommitments, when a manual ledger is associated with an automatic ledger, only the manual ledger is updated.