BADI for MIGO

Hi,

I am trying to give a error message in the MIGO document using BADI CHECK_ITEM.  The requirement is if the field in a PO line item (elikz) is checked, then I just want to send a error message and stop the process of posting. 

Please let me know how I should be getting the values from the MIGO program to do the validations. When I use a select statement to fetch the values, it is only recognising the line item.

Thank you very much.

Padma