2.5D Projectile Help

I'm working on a 2.5D game for senior project at my school. I have the script working to where it instantiates the object I am using. However, I have two issues (that may very well be related).

1) I keep getting this error

NullReferenceException: Object reference not set to an instance of an object PlayerAttack.Update () (at Assets/Scripts/PlayerAttack.cs:90)

I understand that it's telling me something isn't right at line 90, but I cannot figure out why it's throwing the error.

2) The force I'm adding the the projectile doesn't seem to be working. I even disabled gravity on the rigidbody to see if that made any effect (it didn't).

Any pointers in the right direction would be greatly appreciated!

Here is the code I am working on

 #region Notes Section
 /*
 
 Author: Paul Christopher
 Use: This code will:
         -Handle the different attacks(or spells) a player will have at their disposal
         -Check to see if the player is switching (or switched) to a different spell
         -Keep track of the zone the player is in and allow only a certain number of spells to be used (Functionality will be added later on)
         -Instantiate the prefab or particles to show the attack to the player
 
 Notes: None at this time
 
 */
 #endregion
 
 
 using UnityEngine;
 using System.Collections;
 
 public class PlayerAttack : MonoBehaviour {
 
     #region Variables
     //Variables for different HUD based things 
     int health, magicLevel, slavesFreed, zoneNumber;
     public int attackNumber = 1;
 
     //Projectile speed
     float bulletSpeed = 100;
     //public Rigidbody projectile;
 
     //Variables to hold the different attacks
     public GameObject fireProjectile;
     //GameObject projectile;
 
     //Projectile Test Variables
     public GameObject projectileSpawn;
     #endregion
 
     #region Start
     // Use this for initialization
     void Start () {
     }
     #endregion
 
     #region Update
     // Update is called once per frame
     void Update ()
     {
 
         //Checks for keyboard input to cycle attack number down
         if (Input.GetKeyDown(KeyCode.Q))
         {
             //Cycles number as long as it is greater than zero
             if (attackNumber > 1)
             {
                 attackNumber -= 1;
             }
         }
 
         //Checks for keyboard input to cycle attack number up
         if (Input.GetKeyDown(KeyCode.E))
         {
             //Cycles number as long as it is less than 6
             if (attackNumber < 6)
             {
                 attackNumber += 1;
             }
         }
 
         if (Input.GetKeyDown(KeyCode.Space))
         {
             //Test 1
             //Instantiate(fireProjectile, transform.position, Quaternion.identity);
             //Rigidbody rb = fireProjectile.GetComponent<Rigidbody>();
             ////rb.AddForce(500, 200, 0);
             //rb.velocity = (transform.right * -1) * bulletSpeed * Time.deltaTime;
 
             //Test 2
             //Rigidbody instantiateProjectile = Instantiate(fireProjectile, transform.position, transform.rotation) as Rigidbody;
             ////instantiateProjectile.velocity = transform.TransformDirection(new Vector3(500, 5, 0));
             //instantiateProjectile.AddForce(500,10,0);
 
             //Test 3
             //Instantiate(fireProjectile, transform.position, Quaternion.identity);
             //fireProjectile.transform.position += new Vector3(10, 0, 0);
 
             //Test 4
             //Rigidbody hitPlayer;
             //hitPlayer = Instantiate(fireProjectile, transform.position, transform.rotation) as Rigidbody;
             //hitPlayer.AddForce(new Vector3(-1000, 0, 0));
             ////hitPlayer.velocity = transform.TransformDirection(Vector3.forward * 500);
             //Destroy(this.gameObject);
 
             //Test 5
             //Transform clone;
             //clone = Instantiate(fireProjectile, transform.position, transform.rotation) as Transform;
 
 
 
         }
 
         //Handle 
         switch (attackNumber)
         {
             case 1:
                 break;
             case 2:
                 break;
             case 3:
                 break;
             case 4:
                 break;
             case 5:
                 break;
             case 6:
                 break;
         }
 
     }
     #endregion
 
     // END OF FILE BELOW
 }
 

The specific area I'm having an issue with is here:

  if (Input.GetKeyDown(KeyCode.Space))
             {
                 //Test 1
                 //Instantiate(fireProjectile, transform.position, Quaternion.identity);
                 //Rigidbody rb = fireProjectile.GetComponent<Rigidbody>();
                 ////rb.AddForce(500, 200, 0);
                 //rb.velocity = (transform.right * -1) * bulletSpeed * Time.deltaTime;
     
                 //Test 2
                 //Rigidbody instantiateProjectile = Instantiate(fireProjectile, transform.position, transform.rotation) as Rigidbody;
                 ////instantiateProjectile.velocity = transform.TransformDirection(new Vector3(500, 5, 0));
                 //instantiateProjectile.AddForce(500,10,0);
     
                 //Test 3
                 //Instantiate(fireProjectile, transform.position, Quaternion.identity);
                 //fireProjectile.transform.position += new Vector3(10, 0, 0);
     
                 //Test 4
                 //Rigidbody hitPlayer;
                 //hitPlayer = Instantiate(fireProjectile, transform.position, transform.rotation) as Rigidbody;
                 //hitPlayer.AddForce(new Vector3(-1000, 0, 0));
                 ////hitPlayer.velocity = transform.TransformDirection(Vector3.forward * 500);
                 //Destroy(this.gameObject);
     
                 //Test 5
                 //Transform clone;
                 //clone = Instantiate(fireProjectile, transform.position, transform.rotation) as Transform;
     
     
     
             }