Why can't I get to my Borderlands DLC even though I redownloaded it?

After getting the corrupt DLC message in Borderlands for Xbox 360, I followed a solution and 1) Re-downloaded The Secret Armory on XBL Marketplace, and 2) Used my Double Game DLC Disc to redownload The Underdome and Zombie Island. Now since I use my dad's XBL account for multiplayer and my offline account for singleplayer, I downloaded The Secret Armory via XBL. I used my account to download the other two via the DLC disc. The Underdome and Zombie Island works fine, with all my data there, but I still cannot get to The Secret Armory. Can somebody help me on how to get it back?