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.