Bummer! Were there any other hints in the error message?
I've gone ahead and updated the download instructions for Mac users. Please reference this and let me know if it helps.
Unfortunately that was the entire content of the message. I read the download instructions and tried right clicking > Open as well as Ctrl + right click > Open, but I always get the same error message. My "Security & Privacy" settings are set to allow apps from anywhere, and the app doesn't show up as blocked in that section of my preferences. I'm afraid I don't have enough knowledge of mac app development to further troubleshoot the issue. FWIW, I'm on OS X El Capitan (10.11.6).
Sorry for the late reply! I realize the chances that you're still maintaining this game are pretty low at this point, but I hope this helps in future projects.