using FindGameObject with tag to accessing script on a game object

Question

FindGameObjectWithTag is not accessing the script to initialize the variable I am using to store the script.

I have script checking if a power up is active and another setting the boolean variable that activates a power up on the collision. Through debugging I know the collision is working but for some reason I am getting the error above.

The game object tagged as "Enemy" is instantiated to the screen via code but I made sure to only perform the collision that activates the power up AFTER the object was instantiated in the game.

The power up check script is as follows:

using UnityEngine;
using System.Collections;

public class PowerUp_Check : MonoBehaviour {

    //burst script on enemy
    //time on main camera
    //shield on main camera
    //score on main camera
    //clear screen on main camera (for now)

    //state variables
    public static bool pu_burst;
    public static bool pu_time;
    public static bool pu_shield;
    public static bool pu_score;
    public static bool pu_clearScreen;

    //references to scripts
     private Burst burst;
     private IncreaseTime increaseTime;
     private Shield shield;
     private IncreaseScore increaseScore;
     private ClearScreen clearScreen;

    // Use this for initialization
    void Awake () 
    {
        //none of the power ups start out as active
        pu_burst = false;
        pu_time = false;
        pu_shield = false;
        pu_score = false;
        pu_clearScreen = false;

        burst = GameObject.FindGameObjectWithTag ("Enemy").GetComponent<Burst> ();
        increaseTime = GameObject.FindGameObjectWithTag ("Camera").GetComponent<IncreaseTime> ();
        shield = GameObject.FindGameObjectWithTag ("Camera").GetComponent<Shield> ();
        increaseScore = GameObject.FindGameObjectWithTag ("Camera").GetComponent<IncreaseScore> ();
        clearScreen = GameObject.FindGameObjectWithTag ("Camera").GetComponent<ClearScreen> ();
    }

    // Update is called once per frame
    void Update () {

        if (pu_burst) {
            burst.enabled = true;
            print ("Burst active");


        }
        else
            burst.enabled = false;
    //----------------------------------------//
        if (pu_time)
            increaseTime.enabled = true;
        else
            increaseTime.enabled = false;
    //----------------------------------------//
        if (pu_shield)
            shield.enabled = true;
        else
            shield.enabled = false;
    //----------------------------------------//
        if (pu_score)
            increaseScore.enabled = true;
        else
            increaseScore.enabled  = false;
    //----------------------------------------//
        if (pu_clearScreen)
            clearScreen.enabled = true;
        else
            shield.enabled = false;
    }
}

The script performing the activation is as follows:

using UnityEngine;
using System.Collections;

public class MissileDestroy : MonoBehaviour {

    //This script is to be attached to the missile
    //If the missile hits an enemy, that enemy is to be destroyed

    public GameObject blueFlame;


    // Update is called once per frame
    void Update () 
    {

    }

    void OnCollisionEnter(Collision other)
    {
        GameObject flame;

        if (other.gameObject.tag == "Enemy") {

            //show a blue explosion after killing enemy
            flame = (GameObject)Instantiate (blueFlame, transform.position, Quaternion.Euler (0,0,0));

            //the enemy is no longer alive
            EnemyHealth.alive = false;

            //destroy the enemy
            Destroy (other.transform.parent.gameObject);

            //destroy the missile
            Destroy (gameObject);

            //add 100 points to the score
            GameState.score += 100;


        }

        else if (other.gameObject.tag == "isBurst") {
            print ("Collision entered");

            PowerUp_Check.pu_burst = true;

            Destroy (other.gameObject);

        }
    }


}