Hi,
What is your issue and which issue, you want to fix.
And how is your issue relates to purchase order for accout maintence!
If your issue relates to clearing the GR/IR balances,then use transaction code MR11 (used for
month-end or year-end process)but during posting a journal entry of debiting the GR/IR account
and credits the corresponding accounts triiges which have the opposite entry.
Refer SCN blog for clearing the GR/IR balances.
http://scn.sap.com/community/erp/logistics-mm/blog/2012/03/08/impact-of-mr11-execution
http://wiki.sdn.sap.com/wiki/display/ERPSCM/MR11-+Account+Maintenance+Postings
Regards,
Biju K