You have received some goods from a foreign vendor whose currency differs from yours, and you have created a goods receipt PO for this vendor.

To account for any costs incurred during import, you have created a landed costs document and you have copied the data from the goods receipt PO into the landed costs document.

In the Landed Costs window, on the General tab, in the Currency field, you have switched the setting to Local Currency.

On the Item tab, in the Rate field for an item, you have changed the setting to zero.

However, zero is not a valid exchange rate between a foreign currency and a local currency.