Hello,
I updated the game automaticaly with Steam, I checked the files integrity and all is correct.
I made several tries with only a unmanned pod, an antenna and a solar panel directly on the launch pad before posting on this forum and I never got the check mark on the mission panel (that's why I posted, I wanted to be certain).
Anyway Thank you for the Alt F12 trick, I didn't know about that and it solved my problem. My guess is that my savegame is incompatible in some way with the new version and I'll I to deal with it.
Well the strange thing is that I remember having unlocked the orange fuel tanks in my previous session and it is now locked in another part of the tree... So I guess the rule is not as simple as that.
Many thanks to all of you and to this very friendly forum, Have nice launches and landings !