cancel the receipt of a purchase order with bank document?

Hello,

How I can cancel the receipt of a purchase order with bank document?

If, we dont choose Lettre of credit for a purchase order we can cancel the receipt.

But if we choose a bank document (lettre of credit) than we assign the bank document to the receipt, we can’t cancel it.

Is there any solution for that?

Than’s in advance.

Zoheir.