Mass Effect Bring down the sky

Hi. 🙂  When I start Mass Effect, I don't have mission "bring down the sky". I mean it's in folder, I can see credits if I want to, but when I want to play this mission it just doesn't appear. I tried install this DLC on my own, but installer doesn't see Mass Effect at all. Can you help me with this? I really want to do all missions and this one is quite important. And interesting.