Can't add even newly created C# scripts

“Can’t add script behavior AssemblyInfo. The script needs to derive from MonoBehavior!”.
That error appears every time i try to add a C# script (new or edited) to a object (I’m following the resocoder’s AirHockey game tutorial to get some insight on C#, but it really doesn’t have nothing to do with the bug).

This is a weird one…

Does the name of the script match the name of the class?
I.e. the script is called “PlayerScript Wow.cs” instead of “PlayerScriptWow.cs”.

Has the editor compiled (you can see it by checking if there is a loading/rotating icon at the bottom right of the Editor Window)?

Have you tried to reboot the editor?
Sometimes I get weird errors and glitches and by closing and opening the project again, they get fixed.

Let me know if any of this helps, otherwise I’ll think more on what could be causing the issue, and see if anything comes to mind…