Maybe you don't have authorization to update plant data for the plant the MRP controller is relevant for. There are more levels to authorization checks that just the tocde and you are getting an authorization failure message back so you will have failed some authority object check.. As was suggested above you need to use tcode su52 to find out exactly what authorization you are missing. Run your program again then after you get your error message back go to su53 which should contain details of the authorization check you have failed. Send a screen shoot of this to whoever manages authorizations in you system.