Code Error "Can't add script behaviour AssemblyInfo. The script needs to derive from MonoBehaviour!"

I am working on a course where the code is provided but the lecture is outdated and when I try putting the code on an object I get the error “Can’t add script behaviour AssemblyInfo. The script needs to derive from MonoBehaviour!” Please help.

Project:
https://drive.google.com/drive/folders/1F8o104xm7X161f2deAdJv0Mueo-nEc1C?usp=sharing

using UnityEngine; // unity's collection of scripts
using System.Collections; // microsoft's scripts, including coroutines (special type of functions)

public class Manager : MonoBehaviour // class must have the same name as file, also we are extending the monobehaviour class
{
    public float translation_speed_factor; // speed of hero movement
    public float rotation_speed; // speed of hero turning
    public float jump_speed; // jump height
    public float gravity; // gravity applied

    public Transform hero; // our main character to be assigned in Editor
    public Transform env_sphere; // the environment sphere
    public AudioClip jump_sound; // sound to play on jump

    private Vector3 move_direction; // character movement in space

    private Animator animator; // the Mecanim controller
    private CharacterController character_controller; // the character movement controller

    void Start() // this is called on the frame the script is enabled
    {
        animator = hero.GetComponent<Animator>(); // get the component of the Mecanim controller
        character_controller = hero.GetComponent<CharacterController>(); // get the component of the Character Controller
        env_sphere.gameObject.SetActive(true); // enable the environment sphere
    }



    void Update() //this is called on every frame
    {

        float up_down_ctrl = Input.GetAxis("Vertical"); // assign a float variable that goes from -1 to 1 for movement
        float left_right_ctrl = Input.GetAxis("Horizontal"); // assign a float variable that goes from -1 to 1 for turning
       
        animator.SetFloat("rotation", Mathf.Abs(left_right_ctrl)); // set Mecanim's rotation variable to the absolute value of GetAxis
        animator.SetFloat("translation", Mathf.Abs(up_down_ctrl)); // set Mecanim's translation variable to the absolute value of GetAxis
        move_direction.y -= gravity * Time.deltaTime; // apply gravity per second
       
        character_controller.Move(move_direction * Time.deltaTime); // character controller's movement function implemented with our controls


        if (character_controller.isGrounded) // is the hero currently touching the ground?
        {

            move_direction = new Vector3(0, 0, up_down_ctrl); // move the character back and forth on the Z axis
            move_direction = hero.TransformDirection(move_direction); // make the movement relative to the character and not the world
            move_direction *= translation_speed_factor; // multiply the -1 to 1 value by our factor

            if (Input.GetButton("Jump")) // if the jump button in the player settings is pressed
            {
                move_direction.y = jump_speed; // set the jump speed
                animator.Play("jump"); // play the jump animation once
                audio.clip = jump_sound; // set the sound that we want to play
                audio.Play(); // play the sound

            }

        }

        // Rotation :
        // Multiplies the -1 to 1 GetAxis value by the public rotation_speed variable so we can change it in the editor
        float rotation_amount = left_right_ctrl * rotation_speed;
          rotation_amount *= Time.deltaTime;
        hero.Rotate(0, rotation_amount, 0); // ...and finally rotates the hero


    }



}

I’m not sure what the script you showed has to do with the AssemblyInfo script, but the error means your AssemblyInfo script doesn’t inherit from MonoBehaviour. Just like you see in the script you posted next to Manager :

This is the same error I’m getting. Here’s the trick, the script I’m trying to add to my game object IS NOT NAMED AssemblyInfo.cs. It’s named Chunk. I’m adding it to a game object named Chunk, the class is named Chunk, and it is derived from mono behavior. So The question becomes, Where in the hell is AssemblyInfo.cs coming from, when it’s not a part of my project, my game object, or my script?