Hey Pimentoso, it's probably complaining because it's a non Mac store app. Try ctrl-click/right clicking it and opening from that menu. https://support.apple.com/kb/PH18657?locale=en_US
It's actually the first thing I tried, no luck :(
Hmm, that's annoying. :( Can you send a screenshot of the error message to contact [at] samuraipunk.com and we'll look into it for you?