Well, his excuse the last time around was that they misinterpreted 'earthquake' as meaning an actual earthquake (an honest mistake), when they should have interpreted it as meaning people would be shaken with fear at the promise of the end of days. They also claimed that God had been impressed by the efforts of the faithful and so had decided to spare the rest of humankind the agony of the final judgement, instead preferring a quiet judgement period. Furthermore, they suspected that this was a deliberate ploy by God to sort out the truly faithful from the unbelievers; when the Rapture did not come on May 21st, only the faithful would continue to believe, whilst the unbelievers would abandon their beleifs.
Like I said - in the face of undeinable evidence that they are wrong, they will twist it in such a way that it proves them right. It's like the old medieval witch 'test': a woman accused of witchcraft was thrown into a body of water. If she floated, she was 'proven' to be a witch, taken out of the water and burned at the stake. If she sank, she was 'proven' to be innocent, in which case she drowned. No doubt the test was created in such a way that the accused woman would die either way, thus removing her from the community and preventing her from being a threat in the future.
people out there. 
