Apparently if you have merged accounts and created a Battle.net account you might encounter issues when logging into wow. Unfortunately, I did merge my account and whenever I try to log into wow I get an error that says "Unable to validate game version." This is linked with the merged accounts from what I have been reading on the wow forums. So DO NOT uninstall and re-install the game. So don't delete stuff it is all blizzard side.
Quoted from Blue.
Each Auth server has a "fingerprint" system. For World of Warcraft, two exists: original WoW account login system and the Battle.net login system. The World of Warcraft one was updated to accept connections from 3.1.0 build 9767. The Battle.net one isn't ready yet.