Partner roles not getting copied from customer.

Hi ,

Partner Roles not getting copied from customer to delivery Document .

we have created one delivery document from a purchase order and when trying to create billing document from that delivery document it is giving log "payer" and ' Bill to party " not maintained.

when checked in partner tab in delivery document these partner roles are not present there . so what can be the probable reason . These partner functions are maintained in customer.

thanks!!!!!!

which customizing seeting to check for this