Yeah, this is an error that seems to happen with some runs. I had a fantastic run with pointman elite on Pink Floyd's sheep (I think I got 100k DON'T LAUGH) and it said I had done it with Mono! Well, firstly, I could get a much higher score with mono!! But if you go back and check your scores, or do it via audiosurf.com/songs you find that your actual score is the one you played with. This usually happens if you have trouble with your internet connection. I think it's just a minor bug.