itween and Windows Phone not working?

Hi,

So, I am trying to port my game to windows phone. And it worked right away building for windows phone 8. Except there's a weird graphical bug...

So I figured I'll try to see if I get the same graphical issue when building for Windows Store, and Windows Phone 8.1. But, instead I got 124 errors complaining on iTween.

So... how come iTween works when building for windows phone 8, but not for windows phone 8.1? I've tried googling the issue but without much results. Everyone just says "in newer versions of Unity, iTween works". Well, it does for 8... but not 8.1? Anyone has iTween working for 8.1?

I rely heavily on iTween so rewriting it all without using iTween doesn't really feel like a good option.

Thanks in advance