Period &1 is locked for company code &2

What causes this issue?

Company code &V2& is locked for period &V1&.

How to fix this error?

You can continue processing by choosing "Enter".
Continuing processing may cause FI error messages if CO cost flows are
logged for company code &V2& in the reconciliation ledger that are
cross-company code, cross-business area or cross-functional area flows
and are therefore reported to FI during reconciliation posting.
These error messages have no influence on the reconciliation posting of
cost flows that affect other company codes.
If you want to carry out the reconciliation posting also for company
code &V2&, you have to re-open period &V1& for company code &V2&.
To do this, you can either enter a period interval containing the
desired periods for the variant of posting period &V3& and account type
&V4&
<DS:TRAN.OB52>Execute</>
Or assign a suitable variant to company code &V2&.
<DS:TRAN.OBBP>Execute</>

Error message extract from SAP system. Copyright SAP SE.