Diagnosis
In simulation period &v1&, you are using a simulationtype, for which the Check Key Date indicatoris set. The simultion period has the status
Bill mass simulation indexes but does not have a validkey date.

System Response
You cannot use the simulation period as it is not valid.

Procedure
This situation can only arise as a result of umpermitted changes to thesimulation period status or as a result of changes made to thesimulation type.
Set this simulation period to status Inactive, Delete masssimulation indexes and use a new simulation period.