I don't have any experience with world of warcraft, haven't played it, or installed on a system so I don't know what else to suggest.

I'm not finding any specific reason for the issue looking through different forums/google but I found the blizzard support page through nvidia regarding world of warcraft.

http://us.blizzard.com/support/artic...6&pageNumber=1

If their recommendations don't help, they also have a link to contact support for further help.