Hey, you remember the 2009 MTG Duels of the Planeswalkers game on 360? Because it's broken now!
I've been playing it offline (RGH console, Proto stealth, connected to live, NXE dash) but when I went online to update it & install the expansions, this happened:

Pressing Accept opens this menu:

Pressing B at any point crashes the console. Hitting continue crashes the console.
I do not own a retail copy of this game (on 360) so I cannot see if this behavior occurs on real hardware, however the game is no longer on the store at all (not even the themes) and it seems like that's where you'd find whatever DLC package this is.
My theory is that we're missing a free DLC package in the vein of the Battlefield "Multiplayer Pack" downloads, which were free content packs that allowed base-game players to see other players' DLC guns, skins and such even if they'd not purchased/installed the expansions themselves.
In the case of MTG, there were paid expansions with exclusive decks. I have those installed. BUT I think the game is trying to get me to install some free compatibility DLC that no longer exists on the XBL backend.
If you own a legitimate copy of this game on 360 (or even PS3, at this point, i'm not picky) then please hit me up and let's see if the behavior persists on a retail 360. My end goal is to solve this problem, repackage the DLC and release it with a guide so that people can play it properly now that its delisted.