Look at your transaction history for the item's component part to see if it is transacting at $0.00.  We run all our M's thru PO's.  When the received quantities were entered it would take the component parts at $0.00 in stead of the unit cost.  I never figured out why it did it but I had to unreceive those parts, close the PO and create a new PO and then receive the quantity again.  It only seemed with in the PO itself.  It hasn't happend in awhile.