Disablement of Scripting on the Activity Business Object
If you check all the appropriate configuration values, and the problem still exists, then try disabling the scripting on the Activity business objects.
Caution: The Action business component has numerous data
integrity checks. Overriding or removing these checks can introduce
subtle errors to the scheduling process.
Note the following recommendations when changing the Activity business objects, especially the Action business component:
Do not change the code around work time and duration.
Do not disable calculated field logic.