We are all human and the interviewer is looking to see how you've handled past mistakes. Don't try to fool the interviewer by stating you've never made a mistake. Instead, state the mistake, how you corrected it and what you learned from it. Don't play the blame game. The interviewer is asking for your mistake not a facility mistake. Avoid the time you may have been involved in a major event, although many of us have been in this situation, it may be a red flag to the interviewer.