Am I missing a using directive or an assembly reference?

(My First Game) I’m creating a 3rd Person Camera for my First Mini Golf Game and I’ve gotten into the habit of checking things often to make sure they work. This error message showed up our of nowhere after running the game multiple times with “camTransform” in the code. Why all of the sudden if it a problem?

Here is my code:

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

public class ThirdPersonCamera : MonoBehaviour
{
public Transform lookAt;
public Transform camTransform;

private camTransform cam;

private float distance = 10.0f;
private float currentX = 0.0f;
private float currentY = 0.0f;
private float sensivityX = 4.0f;
private float sensivityY = 1.0f;

private void Start()
{
camTransform = transform;
cam = Camera.main;
}

private void LateUpdate()
{
Vector3 dir = new Vector3(0,0,-distance);
Quaternion rotation = Quaternion.Euler(currentY,currentX,0);
camTransform.position = lookAt.position + rotation * dir;
}
}

Was this a mistake?

private camTransform cam;