Hi Matt, you'll get that error because of changes that Apple made in the OS that broke MoI. I have released a version 3.1 update of MoI that solves that though, you can download the updated version by putting in your v3 license key here: http://moi3d.com/reinstall.htm . One other thing is that when running on Sierra MoI will only run from the /Applications folder so make sure you put it there before you run it.

- Michael