Same. When I try to enter on the console I get "This code isn't valid. Please enter a valid code." When I enter it on xbox.com it says "There is a problem with the offer associated with this code."
Also from Australia, purchased from Game.
Guys, forget the DLC...Bethesda had release they are working on a patch to fix the problem on PS3...I was not aware this could happen on the 360..
As i said forget the DLC, do NOT install it, it is believed to cause major issues though this is not confirmed..You can get all items from the DLC within the game anyway...
One more time do NOT install the dlc untill the game is patched for this particular problem...