Diagnosis
The system could not determine sufficient planning periods by theplanning calendar to group requirements by planning calendar periodsfor all the requirements planned in the future.

System Response
When a material is planned by using the periodical lot size byplanning calendar, sufficient periods must be calculated to grouprequirements by the planning calendar for all requirements.

Procedure
Rework the planning calendar with which the material was planned, whichmeans calculate new planning calendar periods.
To do this, go to Customizing for MRP, under the activityChange PPC periods.