11i - Fails in OE_DROP_SHIPMENT error

Gurus,

We are running into this error mentioned above.   This is happening in Pending Transactions - MTL_MATERIAL_TRANSACTIONS_TEMP table.

This is happening for Drop Ship POs.   RCV_TRANSACTIONS_INTERFACE .TRANSACTION_STATUS_CODE shows 'ERROR'  for these items but there is noting in PO_INTERFACE_ERRORS table.  So not sure what is happening.

Transaction type in MMTT is of PO Receipt/Received into stores.

This is happening only with few handful items. Other drop ship items are fine. 

When I looked on the support, it says everywhere that we must have quantity on hand to be at least zero for drop ship transactions. But we have never maintained on hand quantity EVER for our drop ship items and it has always been the case.   And, as mentioned above, other drop ship items are fine and they do not have on hand quantities anywhere.