Thanks, that works fine.
So, good news is the project works just fine for me. So it may be an issue with your installation of unity or your machine. Bad news is that means I have absolutely no idea what's wrong :\ sorry
Ok then, I'll look into it and try to reinstall Unity. What is weird though is that we had the problem on both a Windows PC and a Mac laptop. Maybe it has something to do with some weird setting we didn't think of checking. Anyway, thanks a lot for your help ! we'll work on that, and keep you updated if we find the source to the problem (in case someone else ever gets stuck in this situation).