It's been a long slog but you've finally managed to move all your marking from the pending to the completed pile. The only thing left to do is enter the grades on to the computer, and you're ready to collapse into bed.
The last thing you need is some technical glitch that stops you getting into the system. Particularly when it's not just a quirk of the system, but has been specially created by one of your pupils to frustrate you.
But that was the situation facing high school teachers in Clifton Park in upstate New York, when they found they were denied access to the computer network and were unable to input pupils' grades.
It turns out it was the result of a computer application that had logged on using the names of teachers, but then entered false passwords three times in succession, freezing them out of the system.
The program was put together by Matthew Beighey, a 16-year-old computer whizz who has now been charged with identity theft and unauthorised use of a computer.