Diagnosis
You want to create a check for a field that is to be performed at the'BU' point (before the save)

System Response
At the 'BU' point, no further checks are performed at field level. It isonly possible to perform an entire structure check. It is therefore notpossible to create checks for a specific field at the 'BU' point

Procedure
Delete the field name that you want to check, or change the executiontime