Badi:Header and Item data

Hi,

    I am usingBAdI: me_process_po_cust to check (while creating PO) a PO with document type NBPJ(project) has a  PR,if there is no PR I should get error message.

So in the Header I have put code as below.

In the item level I put code like this.

But I am getting error.Can somebody guide me to solve this problem? Regards, Jaheer