Positive and Negative Question:

The worst thing you can do is give an answer or try to pretend these questions do not apply to you. The worst offender is any "weakness" that is really a strength (i.e. "I work too hard") or saying you have never made a mistake (not likely). The reason your interviewer is even asking these questions is to make sure you can own up to your mistakes and learn from them. If you say you have never made a single mistake (which I think is impossible) that will indicate to your interviewer that you can't recognize when you have.