Maintaining Instructions in Customizing 
Prerequisites
The planning delivery schedule instruction contains the set of characteristics that control how planning delivery schedules are created. You must
enter an instruction in the scheduling agreement in order to create or change planning delivery schedules.
You must be careful when deleting instructions from Customizing. If you delete an instruction that has already been entered in a scheduling agreement, the system freezes that scheduling agreement. You cannot maintain any delivery schedules until you change the instruction in or remove it from the scheduling agreement.
Procedure