Why is this happening!?!

why call xbox? if you have a problem with your download, delete it, and download it again

Yeah thats the answer im sure he was looking for. To OP, there is quite a few people with this issue on these forums and I wish I could help you out further than telling you to call 1-800-4my-xbox. I would call and place a complaint if I were you.

I take you've changed your passwords/log in details on your account already?

If you think someone else is on your account then follow the steps HERE

Sorry, what I meant was that the add-on's weren't installing when I put disc 1 in. And the game starts up fine on disc 1, but when I put disc 2 in to install the add-on's, that error code shows up.

And it's for Xbox 360 if that helps

Hi,

I guess you have used the wrong words but I think I understand your issue.

If you install a game from disc you often will be asked if you want to update the game.

Always answer this question with NO during the installation process.

After you have installed the game completely try to start it and you will be asked again to update the game. Now you answer with YES and you'll get no conflict anymore.

Remember that for every game that you install from disc !