PayPal IPN Error: Order Total/Currency Check failed

[fbc]

What causes this? What should I do about it?

During a paypal transaction on your site the received amount didn't match the order total.
                   Order ID: 2384.
                   Order Number: 111_022f778316daab3fe21f5bf3cb6d.
                   The amount received was: 27.84 USD.
                   It should be: 27.84 EUR.

[fbc]

I think changing this in the paypal code should fix it.

// "currency_code" => $_SESSION['vendor_currency'],
"currency_code" => $db->f('order_currency'),