That is Odd. I have tested VoxWav Pro on a Galaxy S2 phone and an Acer Tablet. Both are running Android 4.1.2 without issues.
I suspect it may be a language or TTS issue.
Can you please tell me
1) The actual model of your device and any other information that might be useful, like is it rooted, are you running a custom ROM etc.
2) What are your language settings for text display and TTS ? Do you have any extra TTS engines installed etc.
If you are not running in English, can you please try to set your Android settings to English for both display and TTS and try again and let us know how it goes?
Do you know on what date you purchased VoxWav Pro? If we can't get this sorted I will certainly give you a refund, but with a bit of patience I think we will probably be able to fix it.