Why does Digital Editions 4.5 (for Mac) crash every time I try to open a .acsm file?

Just installed Dig Ed 4.5 on my new MacBook Air, running Yosemite 10.10.5. I went to open a .acsm file I downloaded from school's library. I signed in with my Adobe ID and immediately the app crashed. Tried opening a difference .acsm file, crashed again. Tried restarting my computer, still crashes.

Help?