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I cannot download WOW The Burning Crusade

I cannot download WOW The Burning Crusade
If you have an original World of Warcraft CD, you will also have the required serial key plus the key from The Burning Crusade. If you create your battle.net account, you can add these keys (and thus their accounts) to your battle.net account, which will feature a button to download the entire game.

You can then download and install the game without issues.