Change currency in PO

Hi All

scenario: User has created a PO with currency USD while vendor currency was EUR. It was user's mistake.

Then user entered invoice also. But after that he realized his mistake for currency. He wanted to change currency in PO from USD to EUR. so first he reversed the invoice. Goods receipts was not posted, so no reveresal of GR was required.

But still user is unable to chnage the currency in PO & getting message as Currency can no longer be changed

Message no. 06489

Could you please help me in this.

Regards

Sapmm