Then it's weird, usually the AVNs that don't open (bounce once in the dock and then close) are easily fixed with this method.
The other thing that you can try is to copy the app in the Renpy SDK folder and see if it starts from the Renpy app (you should find it listed there); if it starts regularly, then you can rebuild a Mac executable from the SDK and it should work.
I'm sorry I can't help more because I updated from Steam and it worked without any problem, maybe if you tell me which version you downloaded I can try to follow the same steps to see what's wrong.
The other thing that you can try is to copy the app in the Renpy SDK folder and see if it starts from the Renpy app (you should find it listed there); if it starts regularly, then you can rebuild a Mac executable from the SDK and it should work.
I'm sorry I can't help more because I updated from Steam and it worked without any problem, maybe if you tell me which version you downloaded I can try to follow the same steps to see what's wrong.