how to cancel PO

hello all,

is it possible to cancel a PO that it gone thru from approval procedure and some of PO lines is partially serve?

my scenario:

i tried to make a PO that gone thru the approval procedure, without any document produce that reference to it (GRPO) and cancel it, it is successfull, i can cancel the PO, but if the PO has partially serve i cant cancel the PO anymore. how to cancel this? please guide..

Note i am using SBO2004A SP:00 PL:32

thanks,

Fidel