Harmonix have announced via the official Rock Band Facebook page that the "Metallica Pack 01" DLC has been removed from the marketplace for new purchases.
The pack which was originally released in November 2007 contained three songs from the band's back catalogue ("Ride the Lightening", "Blackened" and "And Justice for All"), has been removed because the license has expired.
We wanted to give you a heads up on an upcoming change to a limited number of older legacy DLC songs currently available in the Rock Band library. When licensing songs for release for any platform, including DLC, agreements include term limits on how long the content may be sold on a given platform. This isn’t specific to Rock Band – it’s something that exists in pretty much all licensing agreements. Now, over 5 years since the release of the first batch of Rock Band DLC, we’re reaching the end of some of the earliest licenses we secured. Our Music Team has been hard at work extending these licenses to make sure that this has as small an impact on the community as possible, but there may be a very limited number of songs that will no longer be offered for new purchases in the Rock Band store. If you have already purchased the DLC pack in the past, the songs will still be available to play in-game, and should you need to redownload them in the future, you will still be able to.
With more licenses set to expire in the future, Harmonix did promise to release a quarterly licensing update to give gamers a last chance to buy any content before it is removed.
Thanks to all of the members of the community that sent in this suggestion.