Greetings, this error occurs a lot; the basic fix to the issue is that you refresh your "data" folder. This folder contains all MPQ's etc, which can edit gamefiles, from your previous servers you've played on. An MPQ is interupting the data files, leading to the game crashing. You can reset your Data files through the official IceCold launcher, which should already be located in your WoW directory (Folder).