You weren't very specific with the things you have tried, so I don't know if you have tried the things mentioned here:http://stackoverflow.com/questions/19067287/freeduino-v0-1-avrdude-stk500-getsync-not-in-sync-resp-0x00It's not for the Mintduino, but it's for a board using the same microprocessor that I assume you used based on the tutorial you linked.