This problem is driving me mad !
I modded the techtree did some try, and it worked well. I shut down my PC, and this evening, when I launch it again, I have this :
Invisible tech .... but don't get me wrong, it still work, I can select them, as you can see on the picture.
Can anyone help me ? It's is really annoying me ...I triple checked my research.txt, but found no error.