The relevant line in ScummVM.
I'll take a look at it for you.
Will report back once I've found a workaround (although this looks like a coding mistake on Pierre's part, maybe. Been a while since I messed with the AGS engine. RN, I work on reviving ScummC, so that maybe one day people can develop another game with a SCUMM compatible engine).
EDIT: I simply commented out the if-statement, recompiled ScummVM and restarted the game. No error message thus far.
My suspicion is that the AGS engine inside ScummVM is somewhat more strict than the default Windows AGS interpreter and that Pierre set an animation value that is out of bounds for the AGS engine inside ScummVM.
The ScummVM AGS engine is based off the "official" AGS engine branch 3.6.0, which is more restrictive compared to branch 3.5 which was used to build this game. As Happy-Ferret said it'd be better to wait for the dev to fix the bug, as a last resort we could add a workaround specifically for this game.
Talking about bugs, I ran into plenty on ScummVM's end when trying to bundle the game.
I don't think the documentation is up to snuff in that regard. It says that, on Mac, to drop the game files into "MyGame.app/Contents/Resources/game". That didn't work for me. I ended up having to create a scummvm-autorun file in the Resources folder and hardcode the path to "/Applications/MyGame.app".
Furthermore, the preferences are always saved as "~/Library/Preferences/ScummVM Preferences", no matter what change the bundle identifier in the Info.plist to.
That being said, I'm almost done with a first version of the MacOS demo app bundle. Gonna upload it tomorrow, once I have an icon for it and tested it on another Mac.
Would be great if Pierre saw that and picked up my work so we could have an official Mac build.