R12.1.3 - Error FRM-40105: Unable to resolve reference to Item LOT_ENTRY.SUBLOT_NUM.

Can you please review below code , we are geeting this code R12.1.3 - Error FRM-40105: Unable to resolve reference to Item LOT_ENTRY.SUBLOT_NUM.

in lot entry form

IF (form_name = 'RCVTXERT')
    THEN       
        IF (block_name = 'LOT_ENTRY')
        THEN
           --fnd_message.DEBUG('Entered into form RCVTXERT');
           IF (event_name = 'WHEN-NEW-ITEM-INSTANCE')
           THEN
          lv_item_num         := name_in('LOT_CONTEXT.ITEM');
          lv_parent_number   := name_in('LOT_CONTEXT.PARENT_LOT_NUMBER');
          lv_lot_num    := name_in('LOT_ENTRY.LOT_NUMBER');
                      
           fnd_message.DEBUG('Item Number '||lv_item_num);
           fnd_message.DEBUG('PARENT_LOT_NUMBER '||lv_parent_number);
           fnd_message.DEBUG('Lot Number '||lv_lot_num);