The problem was that I did not have the plugin included anywhere in my project. I thought this used to work with TweenMax, but I guess I was wrong!
<!--CDN link for the latest TweenMax-->
<script src="http://cdnjs.cloudflare.com/ajax/libs/gsap/1.12.1/TweenMax.min.js"></script>
<!--CDN links for the latest CSSPlugin, and EasePack-->
<script src="http://cdnjs.cloudflare.com/ajax/libs/gsap/1.12.1/plugins/CSSPlugin.min.js"></script>
<script src="http://cdnjs.cloudflare.com/ajax/libs/gsap/1.15.1/plugins/ScrollToPlugin.min.js"></script>
<script src="http://cdnjs.cloudflare.com/ajax/libs/gsap/1.12.1/easing/EasePack.min.js"></script>