The most common reason to reopen a pay period is to void and re-issue a check. After making the necessary changes, you should close the pay period again and rerun the AP Ledger Update to flag the period as having a complete final update, even if there are no change to any of the other ledgers.

It is important to use caution when making changes, as you want to make sure limits are not exceeded because of changing amounts which have been processed in later pay periods. If limits are involved, remember to re-process all subsequent pay periods for the employee so that they are also corrected.