Type in: C:\ProgramData\Battle.net
Delete the three folders inside.
Then run WoW again, you will get the "Checking for updates" BS again but it will finish it instead of giving you an error message and bring up the screen with the news and the "Play" button. If you can't delete the "Agent" folder, delete everything inside it you possible can, then you should be able to play!
Please share this so people can find out!