They don't think you're a tourist, so you need a proper visa to stay longer. I know that in the past they didn't care and people lived literally for years just on visa waivers + border runs, but this isn't the case anymore.
they want only "real" tourists to come on visa waiver/tourism visa, while everybody else is also welcomed, but with an appropriate visa. The OP clearly isn't a tourist, as he mentioned wanting to get the DTV, so he's planning to stay in Korea for more than 3 months, maybe continously.
I know it's odd they don't disclose what data exactly was incorrect, but besides the name (including middle name, etc.) sometimes there are problems with the date of birth, etc.