SAP Message AJ113 - Not permissible to change rate category in period-end billing period

Diagnosis You wish to execute a period-end billing. The period-end billing coversthe period &v1& -- &v2&. In this period you have changed the ratecategory for the installation from &v3& to &v4&. This change is notpermitted. Procedure Ensure that the rate category for the installation is not changedduring the period-end billing period.