Tomorrow the FM event ends and there is an interval of one day to be able to play without problems, on Monday a multiplayer event begins again for a week, we all hope it will be the last one
There's currently a full marks event on at the moment.
The error message is caused by having the "gems/coins cost 0" hack on, which doesn't interact well with events such as carnival, club constellation and in this case, full marks. Turning that off before entering the game (and only turning it on when you need to use it) should help if you see a similar error message again.
Usually it is highly recommended that mod users don't log in during full marks anyway, as you could get caught. Luckily for you it looks like you are in year 1 so the chance of being caught is low.