Cannot reverse PO encumbrance while saving Credit Voucher

Hi,

We are on PeopleSoft 9.2. User is trying to create a credit voucher ( adjustment ) for PO line 1( associated receipt). On trying to Save, the system throws message : "The related PO XXXXXXX line 1, schedule 1, distribution 1 has been finalized. The encumbrance will not be reversed." The Adjust Mtch values/Encumbrance checkbox ( on invoice line) remains unchecked. Voucher is saved with a new voucher ID.

On the PO side, the PO line 1 is closed. PO Line1-The Final checkbox is checked and Commitment Control Close flag is checked too. When the Undo Finalize button is clicked( on the PO header), system throws chartfield invalid error- "Activity ID XXXXX is invalid".