If you're trying to delete, add or update records in a period that has been reconciled (or in a period prior to a reconciled period) - the system will stop and protect that period as it might unreconcile that period.

Closed Periods
When a period is reconciled, that period and all preceding periods are marked as closed.  No entries can be made to those periods.

To re-open a period
If you are sure that you need to make an entry to a closed period, you will need to re-open that period - and any other periods that are after it.

From the main menu select Reports > Unmark a Reconciled Period

Then select one period at a time and click on 'Unmark a Period' from the toolbar.

Tip: Remember to rerun your reconciliation reports starting from the earliest period that you opened, sequentially up to the most current period that you opened. 

For example:
If you needed to make entries into April 30, 2027, you would need to re-open both:
--the period ending April 30, 2027, and 
--the period ending May 31, 2027
(note: the order of your re-opening does not matter).

Once you are finished, remember to rerun the reconciliation reports.
When running the reconciliation reports, the order DOES matter.
Run your reconciliation reports starting from the earliest period that you opened (here April 30, 2027), sequentially up to the most current period that you opened (May 31, 2027).