Error Update 18273

I recently decided to jump back on to the MoP servers to see if enough has changed for me to play again, only to discover that I can't get it to run. Every time I attempt to run the exe it says there was an error loading an archived update file and then it closes. I've tried deleting the file to force the program to find it and I've checked to ensure everything has the correct permissions but the problem still persists. Is there a way to fix it that I've missed? I really don't want to download the game over again.