Firstly, I have already run through the steps provided in the thread Problems with Blitz songs? look here first! by the very helpful jibjqrkl. After downloading the game, I was never asked to download the track pack and it is not sitting in my download queue.
I am running the Xbox 360 version, and I have previously purchased this title. Since then, I have switched to a different console and was redownloading this game on to my new console. I can download the free pack "Rock Band Free Pack 01" and see the tracks listed within Rock Band Blitz. I am never prompted to download the Blitz Track Pack.
I have deleted the files "Rock Band Blitz Library File", "Rock Band Blitz Audio/Video Settings", and "Rock Band Blitz" from my hard drive. I then reset my console and redownloaded "Rock Band Blitz" and started it back up and still I have no prompt to download the Blitz Track Pack.