An add on won't work...?

I bought an add-on on one xbox, (I have three) and then recovered my account onto another so I could get the add-on on that xbox, the one my brothers usually play on. Neither of them have gold, that's why I had to do the recover thing. Anyways, it downloaded fine, but now my brother can't play it. His account doesn't even recognize it's downloaded, it seems. Also, it's Fallout 3 (Mothership Zeta).