packing slip not found while invoicing the purchase order


i have multiple packing slips against a purchase order (with status RECEIVEd) but when i try to invoice that purchase order, i cannot see those packing slips .

these all are available in inquiries but its not available for matching with invoice.

this is happening only with few items.

when i took few inquries of line items. item detail>>select item…press transaction button…i cannot see any transaction for this PO on this window.

i tried to drill down LOT transaction for this PO line item but cannot trace that as no detail is available.

please help me to fix this.