I once had a schematich for armtech that the game would not let me learn.
I was above the required level but it insisted I did not have high enough level to learn it.
I noticed that it listed 2 requirements, one was the armtech level and the second one was blank.
I think it was a glitch and after a couple of weeks of carrying it I got rid of it, i thought that witn time it would reset or something but that never happened.