If you have the 64-bit client you need to remove it prior patching to the new version of the game, which will be launched today/tomorrow or the patching will result in an internal error. See the blue post below.
„If you are currently testing the 64-bit client, in order to patch up to 4.3.3 you will need to remove the 64-bit files to allow the patching process to complete. With the 64-bit client files in place you will receive the error: Blizzard Updater failed with an internal error.
Simply delete the 64-bit files listed below from the World of Warcraft folder, and the patching process will resume after going through a short repair process.
World of Warcraft-64.app
A new version of the 64-bit client files will be available for 4.3.3 after the patch is live. Please keep an eye on the 64-bit client forum thread for updated files.“
I’ll post the new files as soon as they are up.
Updated for 4.3.4
In case you need a quick reminder on how to install the 64-bit client check here.