LSMW_PO Error

Hai Gurus,

Anybody having exposure to LSMW BAPI method for PO upload?please give me some input (Any document available).

In this method how to set identification field?how to configure to upload sequential file?

I created LSMW using following details

Business Object BUS2012

Method CREATEFROMDATA1

Message Type PORDCR1

Basic Type PORDCR101

while reading data(9th step) i am getting following error

****Identification specifications missing for source structure 'ZHDR'.

****Message no. /SAPDMC/LSMW_OBJ_070013

it is very urget pls help on this