Cannot download both Read Dead Redemption (XB360) and Undead Nightmare (XB360) onto my...

Hey I appreciate you being willing to help me out, but it seems you aren't even reading what my issue is. Your answers are either not helpful, or simply repeating what I've already said. My issue is I can't have both games downloaded at the same time. If I have RDR downloaded, and I am playing it, and I want to play UN, my only option is to uninstall RDR, and then install UN in order to play it. Then if I want to go back to playing RDR, I need to uninstall UN, then download RDR. The answers I am looking for are:

1. Why is this happening?

2. Is there a fix? / Is it possible to have both of these games / campaigns / whatever you want to call them, downloaded onto my SX at the same time

Thank you

You cannot use disc based DLC with BC

as I recall the disc udead nightmare is a standalone product

I don't understand your response, I have each game on separate discs, in their own individual cases. Not the bundle pack that came with both games in the same case. Also as I said in my post, UN downloads and plays just fine as long as the RDR base game is not installed on my SX, and vice versa

I’ve also tried reinstalling red dead redemption alone with undead nightmare still installed.

I tried reinstalling undead nightmare with red dead redemption still installed.

I tried reinstalling both.

None of these things work.