Hi, I downloaded the game again and am getting the same error. I looked into the files and there is no file at this location, so perhaps that's missing from the executable?
SlamFighterII-Mac64.app/Contents/Resources/Data/data.unity3d
also, I'm super sorry about the delay in fixing this; the project is from 2017 and I've been having a hard time getting it to build again! If you can get me your purchase ID, I'll happily initiate a refund. You can tell me here or via email, info@teamdogpit.com -- also, if you get me your email/email me, I'll give you a key to my other commercial release, The Cherry Orchard, for your trouble. Again, apologies!