Requisition in USD and PO in PKR ??

Hi ALL,
Hope you all fine, I just wanted to know one thing from u people, I have maked the Non Catalogue Requisition using iprocurement and currency over here is in USD. While creating the PO using autocreate form in the PO i have select the Supplier and corresponding site in which currency is defiend as PKR.

So, the currency PKR is defualted in the header level of the PO, now while i am approving the PO it gives me the error of distribution rate date. therefore under the same PO i went in the Distribution -> More and the Rate Date field that was blank, thereafter i have maked the change the rate date feild which is automatically the rate field automatically filled based on the conversion. The PO gets Approved too.