On arrival on Friday VOA officer rejected the $50US saying it was invalid and had to pay $42AUS. After some time he explained that the note was too old. On return to Aus yesterday, went to Amex booth and explained situation. They did advise the note was too old and should not have been given to me and happily exchanged. He did explain to me that US notes should have colour across parts of the note and this old one didn't. NOTE: please take a good look at the US notes when you receive them.