There are in fact 3 types of Garmin TTS voices albeit all with the file extension .vpm. I'm quite sure Samantha only came as TTS3 which your modern device should be using. If the wrong one is loaded then either you'll see the incompatible audio message or the device may even freeze on the start screen and be soft-bricked. I'm unsure why you aren't being offered other EN voices by GE or WU. Perhaps you should post the file "English_American_Samantha.vpm" to help identify which file-type it is. Voice files aren't locked by the way.