Sorry if I wasn't clear, but it isn't a problem with Schedule Margin Keys.
The problem is with the dates between PRs (that are STOs that MRP generates) in plant DL01 asking to production plant PR01.
That is because in STO the delivery date of material is for example 05.10.2015 but if I look in MD04 for PR01 plant there is a PchReqRel with requeriments date 04.09.2015 and delivery date 05.10.2015, but PR01 manufactures it for 04.09.2015, which is the the requirements date and we need it manufactures for the delivery date that is 05.10.2015, so the production plant delivers before the delivery date.
Do you know why that could be happening?