Impossible to fly mission 1

[Kimu]

I just installed the campaign and when I want to start it, mission 1 always jumps to de-briefing, as if I had flown it. If I select to fly it again, it tells me that I will lose what I have achieved, and the de-briefing returns.
What I can do?

[_Spad_]

Weird. Maybe uninstall and reinstall it?

[baltic_dragon]

Check if you have no 3rd party mods installed and active, this messed things up for quite a few people. And try to run a repair, I think nobody else had such a problem with M1.