My building is not working

Hi guys, i'm new on unity programming and i'm trying to build my first game, but i'm getting several errors, and mostly are these Error CS0246: The type or namespace name "MonoBehaviour" could not be found. Are you missing an assembly reference?

All of my scripts are getting this error. this is one of my scripts to show you whats going on:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class Laser : MonoBehaviour {
[SerializeField]
private float _speed = 10.0f;
public GameObject laser;
// Use this for initialization
void Start () {

}

// Update is called once per frame
void Update () {
transform.Translate(Vector3.up * _speed * Time.deltaTime);
if(transform.position.y >= 6)
{
Destroy(laser);
}

}
}

 

Are you getting these errors in Unity's console? Does this happen when Unity goes to automatically compile your scripts when you switch back to Unity, or when you press the Build button on the BuildSettings window?

https://docs.unity3d.com/Manual/BuildSettings.html

 

Yes i'm getting on the console. It happens when I try to build, then nothing happens and those errors appears...

 

Is your script name identical to that of your class, Laser.cs?

 

Yes, it's

 

well, good news, i've just update my Unity and now it works fine hahah, Thank you guys anyway!