How to reverse PO packing slip from prior closed period?

Hi,

I have a problem when i tried to cancel the product receipt/POpacking slip that received in Aug (now Aug fiscal period set to on hold). The system show error to me

"Message (02:55:08 pm)
Tracking dimension has been automatically selected for correction.
Posting
      Purchase order: PO000765
      The packing slip correction cannot be posted to the original accounting date when the fiscal period is closed. The accounting date has been moved to the first day in the next open fiscal period. ==> and system read the accounting date = 01-Oct-2012
      Fiscal period for 31-Aug-2012 is not open.
      Posting has been canceled.
An error occurred during update"

I could not the -negative number in receive now, AX2012 not allow -negative receive now.

Please suggest on how i can reverse this packing slip (i cannot open August period) and thanks in advance.

Thanks and regards,

TK