Error 2579 - For pupils no longer on roll the attendance sessions possible must be greater than or equal to zero for the second half of the summer term.

This error arises if a student has gaps in attendance between their leaving date and the last day they have student attendance. Please check the leaving date assigned to the student, then look at the attendance data for this student in the month prior and after this date (on the student tab, you can click on the Attendance Date Range report if in the previous academic year. 

Amend the leaving date to the last day attendance data was recorded, then save at the base of the extended tab. Recalculate your census and the Error will have left.