"This session has not happened yet: attendance is taken on the day or afterwards."

Where: Take attendance or Finish, on the attendance sheet.

Why: the session is dated on a day that has not come yet (the school's date, in its time zone). Attendance is taken on the day of the session, at any time, or later.

What to do: wait for the day of the session. For a class moved to another date, the owner can change the session date in Schedule ("This session only").