If you are getting this message box at the beginning of the school year while making timetable changes then you will need to check the TERM DATES for the schools.
*Class drop date uses the TERM dates to determine if it is 5 days AFTER the reporting period.
Please go to Setup, Marks and Comments, Term Dates and edit the dates to be within this school calendar year, once this is correct then when you make changes to the student timetables this pop up box will not show UNTIL AFTER the first report period happens.