Diagnosis
The number of the associated stability study is proposed as theidentifier for the testing schedule.
However, this does not happen if a suitable number range has not beenset for maintenance plans in Customizing. In this case, you must enterthe number of the testing schedule manually.

Procedure
Ask the person responsible to check the Customizing for maintenanceplans in your system, and, if necessary, create an external numberrange for testing schedules for stability studies (same as the numberrange for notifications for stability studies).