Why does Ableton do this?

[DavidStars]

So I'm currently on Mavericks 10.9.5 with Ableton 9.1.6. My computer is a early 2011 Macbook Pro 13'. I've been interested in upgrading to Yosemite for a while now. Looks nice, probably would run smoother, syncs better with my iPhone 6 (I've been having ANNOYING sync problems with iTunes and my 128GB iPhone where it often deletes all the music, but that's another story). So my issue is that I've tried upgrading to Yosemite but for some reason, some of my projects won't open. Most of them will and they don't crash, but I'll get an endless spinning color circle. Happened when I tried to upgrade a couple weeks ago, so I decided to restore from my backup (thank God for Time Machine). But I've tried upgrading again and am looking to solve this problem. All my other programs work fine and most of my projects open fine, but two projects in particular (at least so far from what I've tested) don't seem to open. I've tried looking through the plugins I used in the project, but from what I can remember, they're no different from most of my other projects. Any ideas as to what could be the cause of this and/or how to fix this?