Pianist realises the orchestra has started the wrong concerto…
http://blogs.telegraph.co.uk/news/damianthompson/100243153/pianist-maria-joao-pires-panics-as-she-realises-the-orchestra-has-st

"This is quite extraordinary. The wonderful Maria João Pires is ready to play a Mozart piano concerto with the Amsterdam Concertgebouw conducted by Riccardo Chailly, only to hear the orchestra begin playing another Mozart concerto – no 20 in D minor, K466, not what she was expecting or had prepared for. Can you imagine her horror? You'll have to watch the film below to find out what happened next."