I cant open MoP

I downloaded the big MoP version, and when I try opening it it gives me the message:

Data/enGB/wow-update-enGB-18273.MPQ: World of Warcraft can’t make a required change to an archive file. Be sure you have write permission for the World of Warcraft folder or try running the game in administrator mode. For more information, see:

Anybody knows why ?

Follow these steps:
1) Restart your PC ( this is important)
2) close your Torrent client and move your WoW folder away from your Torrent's download destination
3) now right click on WoW folder> Properties> remove "read-only".

http://i.imgur.com/5wWKUL6.gif