Maybe it’s the curse of Macbeth. And the law of averages dictates that things must occasionally go wrong in the theatre, and that must occasionally occur in the full gaze of the national critics assembled to report on the occasion.
But pity the poor Old Vic. Two press nights in a row have now been beset by technical glitches: during the opening night of Richard II, the lighting scheme literally lost the ‘plot’ during the first act, and though they soldiered on to the interval in reduced lighting, an announcement was made then that an area-wide power surge had caused the difficulty, so we were not seeing the production in its best light, so to speak.
Then last night, a key set change failed to occur during the first act of Aladdin, and a black-tied stage manager had to walk into the middle of that scene to stop it; which led to a tongue-tied Frances Barber declaring, “But I don’t know any jokes!”, and looking lost and helpless like a rabbit caught in the headlights; she started in on a comment about “Richard Wilson is at Wimbledon…”, but we never got to hear her desperately searching for a punchline because the curtain was at last brought in. I can only imagine what her predecessor in the role, Maureen Lipman, would have made of such a moment, though: during last year’s press performance, she responded to a crackling microphone by declaring, “That’s me old bones crackling.”
But if the show is good enough, it survives such mishaps: one of the National Theatre’s biggest-ever hits, the now returned (and Broadway-bound) The History Boys was launched with a press night where the fire sprinklers went off, drenching the set, half an hour before curtain up; when it finally went up, an hour later, Nicholas Hytner took to the stage to tell us that his entire company had been onstage frantically trying to mop it up! The lighting, too, was affected throughout; but nothing could dim Alan Bennett’s wonderful play or the wonderful performances in it.

And don't forget that this time last year the first night of Aladdin was cancelled completely due to technical difficulties:
http://www.london-se1.co.uk/blog/2005/12/what-is-it-with-old-vic-and-its-first.html