World of warcraft error message ?

i downloaded a torrent for the world of warcraft wrath of the lich king, and it wont download. i open up the installer exe and click install on the launcher and i wait until 2% and a message comes up saying when downloading the common file mpq file " sound\creature\deathknightaggro.wav in archive C:\program files (x86)\world of warcraft\data\common.MPQ could not be opened because error 2 occcured. if this presits call blah blah blah" i ndd help!!! and btw its a torrent fle not a cd thing