InvalidCastException: Cannot cast from source type to destination type.

Hello. I'm sorry to be a noob, but I have very little experience in Unity scripting. Can someone please point me in the right direction as to why I'm getting a InvalidCastException error on line 71 of this?

 using UnityEngine;
 using System.Collections;
 
 public class Shot : MonoBehaviour
 {
     public Transform projectilePrefab;
     public Transform projectilePrefab2;
     public float fireRate = 0.5f;
     private float nextFire = 0.0f;
     public float fireRate2 = 0.1f;
     private float nextFire2 = 0.0f;
     private bool shooting = false;
     private bool shooting2 = false;
 
     // Update is called once per frame
     void Update()
     {
         if (Input.GetButtonDown("Fire1"))
             shooting = true;
         if (Input.GetButtonUp("Fire1"))
             shooting = false;
         if (Input.GetButtonDown("Fire2"))
             shooting2 = true;
         if (Input.GetButtonUp("Fire2"))
             shooting2 = false;
 
         if (shooting && Time.time > nextFire)
         {
             Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
             RaycastHit hit;
             if (Physics.Raycast(ray, out hit, 100000.0f) && hit.collider.gameObject.tag != "PlayerShip")
             {
                 GameObject projectile = (GameObject)Instantiate(projectilePrefab, transform.position + transform.forward * 8, transform.rotation);
                 projectile.transform.LookAt(hit.point);
             }
             else
             {
                 GameObject projectile = (GameObject)Instantiate(projectilePrefab, transform.position + transform.forward * 8, transform.rotation);
                 projectile.transform.LookAt(ray.GetPoint(300.0f));
             }
             nextFire = Time.time + fireRate;
         }
         if (shooting2 && Time.time > nextFire2)
         {
             Ray ray2 = Camera.main.ScreenPointToRay(Input.mousePosition);
             RaycastHit hit2;
             if (Physics.Raycast(ray2, out hit2, 100000.0f) && hit2.collider.gameObject.tag != "PlayerShip")
             {
                 GameObject projectile2 = (GameObject)Instantiate(projectilePrefab2, transform.position + transform.forward * 8, transform.rotation);
                 projectile2.transform.LookAt(hit2.point);
             }
             else
             {
                 GameObject projectile2 = (GameObject)Instantiate(projectilePrefab2, transform.position + transform.forward * 8, transform.rotation);
                 projectile2.transform.LookAt(ray2.GetPoint(300.0f));
             }
             nextFire2 = Time.time + fireRate2;
         }
     }
 }

I have searched the manuals and googled the issue for a long time now, but I just can't figure out why I'm coming on this problem.

Thanks very much.