Back-End Error:Enter Plant after PO is ordered

Hi Experts,

         we are getting error Back-End Error:Enter Plant after the PO got ordered. if we check for the errors in the portal  before the PO is ordered shows up no errors but when we order the PO the status in tracking got updated as ERROR IN PROCESS and the error Back-End Error:Enter Plant is showing up. please suggest why this error occurs. the PO here is a Auto generated PO for the shopping cart.

Thanks in Advance,

Thanks& regards,

Aishwarya.M