Dlc problem

It sounds like he bought the DLC under his account, copied it to a flashdrive and gave it to you.

If that is the case, you will not be able to use those DLC with your gamertag since your account is not the one that purchased it.

Thanks I really hope this works, I hate getting that annoying pop up as well

Try this

1.) Sign into your Xbox LIVE account on www.xbox.com, navigate to your account information, and change the contact email address you have on file so that it is different than your current Microsoft Account/ Windows Live ID (The email you use to sign into
your profile).

2.) While still looking over your account information on www.xbox.com, please verify that the address and other information on file (such as your phone number) match the billing information associated with the payment instrument you are trying to add or
use on your Xbox LIVE account.

Once the above steps have been completed, you should be able to resume purchases on Xbox LIVE using valid payment instruments within 24 - 48 hours

from what i understand the peacekeeper will only be available for you she would have to purchase the pack herself

Sorry to hear you're having trouble. What you have described is considered marketplace theft and could result in the gamertag(s) and console(s) being banned permanently from Live. Please be sure to check the terms of use at http://enforcement.xbox.com/

The reason that the content does not work for you is because it belongs to your cousin. If you want to use the DLC you'll need to purchase it for yourself.