Error while posting the Purchase order

Hi All

while posting the Purchase order i am getting the following error

Voucher INV-03532, date 17-Apr-2013, account 11710001, amount currency 14,300.00, amount MST 53,628.43, alternative amount 0.00, currency USD, text

As a primary currency i am using the SAR (Saudi Riyal) and the secondary currency here is the USD (1 USD= 3.754 SAR)

I created the PO in USD.

Please advise me on this.

thanks