Error At Purchase order Invoice posting

Dear Sir,

When I post invoice for purchase order,infolog shows the fallowing message and not allowing to post my invoice. please advise me what to do.

Voucher 110000093_PIV, date 8/09/2010, account 116010121, amount currency 1,175.00, amount MST 1,175.00, alternative amount 313.33, currency SAR, text### Transaction on voucher 110000093_PIV donot balance as per 8/09/2010 (company currency: 0.00 - secondary currency :-0.02)### Posting has been cancelled.### operation cancelled.