I had the same issue and it turns out the App was corrupt. You can download just the App via a link Ka.da posted here. Replace the one in your WoW folder with the new one and try to launch.
https://mega.nz/#!YoskETLZ!JeZR8l8WnWXGSOvni3MLacfuRsymdmeUEaKmv9fOOUw
This fixed my problem.