Hello Liviu,
I noticed a possible issue in FET when using the constraint
A set of activities has a set of preferred starting times.
If I add this constraint with duration = 2, while in fact the file contains no activities of duration 2, FET shows the following error when starting generation the timetable:
Hello, Youssef,
I don't consider this a bug. More like a suggestion. I consider that it is good to inform the user that the constraint is useless and require the user to deactivate it.