I just purchased a Vista Machine, AMD Turion 64. Now I am currently experiencing this same error. With me - which I have not noticed anyone else mention in this thread - the error continuously cycles through without ever stopping. It just keeps going like lamb chop. *see Screenshot*
I run WoW from an external drive (F:\WoW\World of Warcraft) and WAU from it's default install location. I noticed that if I - after reading this thread - only change the permissions to the WoW folder; I continue to get the error. I had to change the permissions to the drive itself (F:\).
I can no longer get the error to occur, however: I am not sure if any updating is taking place as the "Last Change" dates appear to have remained the same.