Sims cannot use "folded" stair

Hi! You see I made set this stair from the 3rd floor to the first as the entrance, and use the stair feature to give it "shape" (Don't really how it is called), and even though I didn't use move objects to place it, my sims can't use it, and I replaced it with a straight normal one, and it works... (I'm attaching a screenshot so you can see it) Does anybody has a clue why it's not possible to use? Thanks in beforehand!