2) A photographer came and took a photograph of me at that particular point in the piece....but then it happened twice...so not a good excuse
Hi,
If you were distracted, and made a mistake because of the distraction, then the next time this part of the piece comes around, you were probably thinking something along the lines of, "Oh I stuffed that up last time, I'd better get it right this time" or "I hope I don't mess up again"
Which are the sorts of thoughts which will guarantee you mes up again.
If you are going to perform the same work again, then you must convince yourself that you can do it without mistakes - in your own mind, you must see and hear yourself always playing it perfectly. Because once you start thinking about mistakes which happened in the past, or mistakes that may happen in the future, then they will happen during the performance.
And then, in the real performance, it doesn't matter if a little slip or two occurs, they occur for everyone. Even a big mistake is not a tragedy - just keep going - because if you keep playing like nothing happened, as lostinidlewonder says, no one will remember the mistake!
Good luck!