Unity started rejecting my scripts?

Hello and greetings. I have been trying to make a game and it has been going well for a few months now. However, when i started up unity this morning, i found one of the scripts apparently had a compiler error. not thinking this was such a big problem, i looked in the script to see it was FPSinput, one of the default scripts that come with unity. it said something about the UnityEditor namespace not being found, so i looked up how to fix it and placed it in addons/Editor. However, trying to playtest gave me the same kind of error again. i didn't think too much of it here because they were all related to the same object (FPSinput, Charactercontroler) but when it started coughing up random scripts saying that they all belong in the editor folder, i started thinking it was weird. especially since everything worked just fine yesterday, when they were in their own folder. can anyone tell me why unity started hating it's own scripts?

Thanks in advance, -bolibob2 :)