Many individuals make the mistake of trying to find the culprit before fixing the error whenever a problem arises. There are several ways to deal with a problem when it comes up and the first step is always to fix it. Maybe you can fix it yourself or maybe you can ask someone else. If finding the perpetrator is quick, go ahead and ask him to fix the problem himself, but don't get mad at him yet, it will only put additional pressure on his shoulders and make him more likely to make more mistakes.
Once the problem is fixed, it's time to review the problem and find out what went wrong so that it doesn't happen again. Every mistake is an opportunity to learn. Maybe a single person was responsible for the error, but no one else caught it either. Is there some way to make it impossible to repeat the error? Do you do enough testing (automatic or manual)? Do you do any kind of reviewing? Or do you simply tell your people to be extra careful?
Don't let people the opportunity of making mistakes and they won't, otherwise you're just as guilty.