Somehow or another it needs to find the contents (the individual files, that is) of VoiceData at the root of mainBundle. I’m not familiar with rubymotion but a frequent source of issues in this kind of situation is with Xcode creating a subfolder in mainBundle rather than copying the files directly to root. You should be able to verify that the files are in the right place by opening up the app product package and just looking in the bundle to see if the files are there and are where they ought to be.
However, I have never tested with rubymotion and don’t actively support it, so I can’t guarantee that the licensed version works with it. If you want to buy a license, maybe consider sending me over a sample app with a test bundle id first so that I can check out whether you’ll be able to make use of a license. You can contact me about this via the contact form when you’re ready.