I just recently downloaded Halo 3 for free on Xbox Live to take it out for an old spin since I had given away the game before. I used to play the game religiously and have downloaded all of the map packs. However, I’m now unable to access all of the content I previously purchased and downloaded from the Heroic Map Pack all the way up to the Mythic pack. I’ve tried redownloading them but nothing seems to work. Any ideas to help me?
Are you playing on a new console from when you last downloaded them? If so you will need to go on xbox.com and do a license transfer to register all your old purchases with your new xbox.
If not, try deleting them, clearing your xbox console’s cache and then redownloading.
Also check your custom content. Halo 3 only allows 100 items of custom, which for some reason also includes the actual DLC maps. If you do have 100 items of custom content, try deleting some, going to the dashboard/turning off your xbox and restarting your game.
These are the only solutions I’ve come across relating to this issue. If none of these work try contacting Xbox Support.
I actually did purchase a new xbox but i configured it with my old Xbox’s HDD. Do I still need to do a license transfer with that?
> I actually did purchase a new xbox but i configured it with my old Xbox’s HDD. Do I still need to do a license transfer with that?
Yes. The purchase license for your DLC is linked to the serial number of the console it was first downloaded on, not the hard drive. Its a pretty simple process that takes a couple of minutes. All the steps you need to follow are on xbox.com.
i had the same problem, purchased the mythic 2 map pack but it didnt show up in game but it said i had bought it 
couldnt be bothered with all thw hassle so i just bought ODST
License transfer is not necessary when you’re signed in online. It doesn’t matter if you’ve change 360’s a dozen times or once. As long as the account that purchased the content is connected to xbox live and contains the content on an appropriate storage device (hard drive being your best bet), the content will work. This goes for all 360 games. The only trouble you’ll run into is loading them OFFLINE without licenses.
Phil is correct about the other stuff though. I’ve made a sort of tutorial to address the custom content on another thread:
https://forums.halowaypoint.com/yaf_postsm2762190_DLC-not-working.aspx#post2762190
That has worked for a few people as far as I know, but I’d try Phil’s other suggestions too, like the cache clearing and so on if the custom content fix doesn’t work for you.
Also, Slashed, try out the custom content thing as well, it beats buying a new disc to play the content…even though you already have, lol
Sorry, one more thing, Phil mentioned that the game counts the DLC as custom content, however that’s not the case. It seems that way but it’s actually counting the content you’ve added without having DLC in the past, plus the content that was already contained on DLC when it was present. I won’t babble on about it here though, it’s explained more thoroughly in that thread 