The first time I made the mistake of using Python (because of its whiteboard value) while not being proficient in it. They really didn't like me Googling some basic stuff.
The second time I still used Python, but had 5 years experience using it behind. Can't be objective but it was probably the best interview I've ever done. Reviewed my code afterwards, and could only come up with minor improvements. Got refused, I asked what could I improve and I got a very generic "not a good match for the team" which, in retrospect, reading your comment, could have been very accurate.