Not a problem specific to dual-boxing

Do a scandisk.

Do a Virus scan.

Run the repair tool.

There is nothing at all wrong with the Wiki guide and there's nothing in your post to suggest that you're doing anything wrong other than jumping to conclusions.

edit: the only thing I do different to you is that I run wow.exe instead of the launcher, because I have KC launch and maximise my clients for me. I seriously doubt that makes any different whatsoever, but if you're stuck then it's worth a shot.