在发货拣配时怎样用这个函数'WS_DELIVERY_UPDATE'

when run the function  'WS_DELIVERY_UPDATE',there is something wrong happend.

the problem is that why the Import parameters vbpok_tab-lgort can't be Imported.

here is the test code:

DATA: vbkok LIKE vbkok.

DATA:vbpok LIKE TABLE OF vbpok WITH HEADER LINE.

DATA: prot LIKE TABLE OF prott WITH HEADER LINE.

vbkok-vbeln_vl = '0080188947'.

vbkok-vbtyp_vl = 'J'.

vbkok-vbeln = '0080188947'.

vbkok-wabuc = 'X'.

vbpok-vbeln_vl = '0080188947'.

vbpok-posnr_vl = '000010'.

vbpok-vbeln = '0080188947'.

vbpok-posnn = '000010'.

vbpok-werks = 'H050'.

vbpok-pikmg = '30'.

vbpok-lgort = '0010'.

APPEND vbpok.

CLEAR vbpok.

CALL FUNCTION 'WS_DELIVERY_UPDATE'

  EXPORTING

    vbkok_wa                           = vbkok

   synchron                           = 'X'

   commit                             = 'X'

    delivery                           =  '0080188947'

   update_picking                     = 'X'

   if_database_update                 = '1'

   if_error_messages_send_0           = 'X'

TABLES

   vbpok_tab                          = vbpok

   prot                               = prot .