GetComponent don't work (i am desperate)

Hi guys, i need you help.

I am working on a script that should assign "OggettoDaMuovere" (Move an Object) when it is instantieted. This is the code:

 using UnityEngine;
 using System.Collections;
 
 public class RetroGameHandler : MonoBehaviour {
     public GameObject ret;
 
     public GameObject tri;
     public GameObject tri90;
     public GameObject maincamera;
     float time2= 1.1f;
     float time;
     int rnd;
     int contaOggetti= 1;
     float conta= 0f;
     GameObject[] ListaOggetti= new GameObject[100];
     // Use this for initialization
     void Start () {
         time = 5;
     }
     
     // Update is called once per frame
     void Update () {
         time = time - Time.deltaTime;
         time2 = time2 - Time.deltaTime;
         if (time2 <= 0.0f) {
             time2 = 1f;
             conta = conta + 0.15f;    
         }
         if (time <= 0) {
 
             time=5f - conta;
             if (time<=1f) time= 1f;
             rnd= Random.Range(1,4);
             switch (rnd) {
                         case 1:
                                 ListaOggetti[contaOggetti] = Instantiate (ret, new Vector3 (GameObject.Find ("Player").transform.position.x,
                                          GameObject.Find ("Player").transform.position.y + 20.0f), Quaternion.identity) as GameObject;
                                 
                                 
                                 break;
                         
                                 
                         case 2:
                                 ListaOggetti[contaOggetti]= Instantiate (tri90, new Vector3 (GameObject.Find ("Player").transform.position.x,
                                            GameObject.Find ("Player").transform.position.y + 20.0f), Quaternion.identity) as GameObject;
                                 
                                 break;
                         case 3:
                                 ListaOggetti[contaOggetti]= Instantiate (tri, new Vector3 (GameObject.Find ("Player").transform.position.x,
                                                                            GameObject.Find ("Player").transform.position.y + 20.0f), Quaternion.identity) as GameObject;
                                 
                                 break;
                                 
                         }
             maincamera.GetComponent<GuiOggetti>().OggettoDaMuovere= ListaOggetti[contaOggetti];
             contaOggetti= contaOggetti +1;
             }
     }
 }

I don't find the error, it works for the first 2-3 time, then it don't.

Here is the code of the second script (hope it can help)

 using UnityEngine;
 using System.Collections;
 
 public class GuiOggetti : MonoBehaviour {
     public Texture2D avanti;
     public Texture2D indietro;
 
 
     public GameObject OggettoDaMuovere;
     float speed = 4.0f;
     
 
     // Use this for initialization
     void Start () {
 
     }
     
     // Update is called once per frame
     void Update () {
         if (Input.GetKey (KeyCode.W)) {
             OggettoDaMuovere.transform.Translate (Vector3.right * speed * Time.deltaTime);
         }
         if (Input.GetKey (KeyCode.Q)) {
             OggettoDaMuovere.transform.Translate (Vector3.left * speed * Time.deltaTime);    
         }
         Rect w2Rect = new Rect (Screen.width - Screen.width / 8.3f,  Screen.height-Screen.height/1.03f, Screen.height / 6, Screen.height / 6);
         Rect a2Rect = new Rect (Screen.width / 10 - Screen.width / 12, Screen.height-Screen.height/1.03f, Screen.height / 6, Screen.height / 6);
         foreach (Touch t in Input.touches) {
                         Vector2 vec = t.position;
                         vec.y = Screen.height - vec.y;
             
             
                         if (w2Rect.Contains (vec)) {
                             OggettoDaMuovere.transform.Translate (Vector3.right * speed * Time.deltaTime);
 
                         }
             
                         if (a2Rect.Contains (vec)) {
                             OggettoDaMuovere.transform.Translate (Vector3.left * speed * Time.deltaTime);
                                 
                         }
                 }
 
 
 
 
 
 
     }
     void OnGUI() {
         
         GUI.Button (new Rect (Screen.width - Screen.width / 8.3f, Screen.height-Screen.height/1.03f, Screen.height / 6, Screen.height / 6), new GUIContent (avanti, "Button 1"));
         GUI.Button (new Rect (Screen.width / 10 - Screen.width / 12, Screen.height-Screen.height/1.03f , Screen.height / 6, Screen.height / 6), new GUIContent (indietro, "Button 2"));
 
         
     }

Thank you if you will help me