How do I fix this?

When I try to download certain challenges I get this after I click fight I believe.

That looks like a challenge that uses a mod or expansion pack that you do not have installed, or possibly one where they have indicated an expansion isn’t used, whereas it actually has been.

I take it I just won’t be able to play challenges from this person then? I have all the DLC packs installed. Also, the challenge was using Rebels so I’m confused. Thanks for the response back Cliff (love the game!)

If you post the challenge number I can crack it open using magic and see what it’s expecting.
The thing is, if people mod their local install, then issue a challenge, the challenge system can’t verify that their module names make sense, so its very likely its someone forgetting they are using modded moduels in their designs.