Voucher Build Process creates the voucher with build error with the error message - Invalid Purchase

Hi, What are the potential scenarios voucher build process creates the voucher in build error and error message - Invalid Purchase Order ? Additional Information When I query the PS_TSE_VCHRLN_FLD (Voucher Line Errors record), the error message refers to "The voucher referenced an invalid Purchase Order. This Purchase Order has not been dispatched, please dispatch the Purchase Order first." But the Purchase Order in the PO header record is "Dispatched". Any inputs on this are highly appreciated. Thanks, Geetha