Hi,
Please re-install World of Warcraft, or try to patch down to 4.0.6, you don't have to use all of the disc to re-install, just download the full game client from the World of Warcraft website and install from there, usually this is caused through a corrupted file and repair doesn't always solve the problem, if that fails I will look into it, for now just re-install the game and post back and see if it fixes the problem..
Thanks..