Quotation has approved but in PO exact supplier is not come on catalogue function ....

in response to our tendor many supplier have replyed along with quotations and after techincal evaluation we have approved the diffrent lines of item of diffrent suppliers ..... now while making PO using Auto creat Function from Requisition we have call the few lines to one supplier who has selected in the technical evaluation ..... now in the lines of PO while i am trying to use catalogue (based on low price) function to select the supplier for unfortunatly that suppler to whome we have selected is not come and inspite difftent supplier are come ....... kindly resolve the issue ....