You have many MPQs and some files can be duplicated in different versions in different MPQs.
So if you extract the wrong dbc file, wow wont start.
To get every time the newest version of all files i extrat ALL wow files to an folder on my HD.
But you have to extract them in the right order. This is described in the post.
You can also use the ad.exe form your emulator to get the latest DBC files.