Emulator for Mac not working

I'm having trouble with the emulator. My students (180) have Macs, and it works for most of them, but not for all. I (and the IT people from my school) have tried everything suggested in the troubleshooting section of the MIT website. It simply won't open. It displays a message related to the aiStarter. We've tried uninstalling and installing again, we've tried EVERYTHING! Does anybody know about another emulator that can work with AppInventor, different than the one that can be downloaded from the website?