I'm having the same, problem. I've been able to complete the action in the save file I was using for the Reaper's Reward event. So It may be something with them editing Grim? (I also am not using mods even double checked and made sure any that I've used have been deleted and tried to repair the game.
It does not let me with a new sim...just the one that Woohooed grim before the expansion was released. It also seemed to work best when my sim became hysterical, However that could very well be a coincidence. Tried again with the original sim, Had to reset both sim and grim several times and attempt a few times as well then it worked
