Quote Originally Posted by 'Talamarr',index.php?page=Thread&postID=195351#pos t195351
After another failure and more research, here's something to try if you get this error: Go to [WoW Directory]\Data\ and delete Patch.mpq (ok, don't delete it but rename it just in case). Then run the repair.exe utility in the wow root folder. It will tell WoW has a critical error and needs to be repaired. Let the repair run (it may take a little while).

Then try running the game again and let it patch.

That's what I'm trying now and will see how that goes.
This worked for me! WOOT!

If you get that error, give this solution a try before trying to reinstall.

Happy 3.1'ing everyone.