Sub Contracting Operation Problem

Hi frnds,

I'm facing problem related with GL Account.

Dears I'm going to create Automatic Purchase Requsition for material which is manufactured Externally by Vendor but the RAW Material is given by us means I want to create Sub contracting PO and only paid service prices for manufacturing the material to vendor. For this

1. I create the PIR through TCODE ME11 with material

2. Maintain the PIR in Master Ricepe with Cost element.

3. Create Process Order & PR is generated but

When I trying to convert PR to PO, it show Error message that the assign GL Account is not correct at

the field Account Assignment.

I want to know at Account Assignment what GL Acc. will come to enter.

Parminder