PO Close...

Hi Guys- 

                 Match status on my PO is 'Partially matched' but with the 'PO' I created a Voucher .The voucher is on Matched status and fully paid ..But still  my PO Match status is'Partially matched' ..what is is the reason for this....?Because of the above reason i am unable to close the PO....

                      PO Amount -  1200 USD

                     Voucher amount- 1200 USD... Voucher id fully matched and paid....   But still PO in 'Partially matched status'......?

Thanks,