UnityException: Tag: Gamecontroller is not defined.@Space shooter tutorial..

Hello everyone..

I'm following the Space shooter tutorial by unity...I got an error while doing Counting points and displaying the score.My game stops and shows me error.

And this is the error..

UnityException: Tag: Gamecontroller is not defined. UnityEngine.GameObject.FindWithTag (System.String tag) (at C:/buildslave/unity/build/artifacts/generated/common/runtime/UnityEngineGameObjectBindings.gen.cs:297) Destroybycontact.Start () (at Assets/Scripts/Destroybycontact.cs:13)

Please help me find the error..

Here is my code for (Destroybycontact script)..

using UnityEngine; using System.Collections;

public class Destroybycontact : MonoBehaviour { public GameObject explosion; public GameObject playerExplosion; public int scoreValue; private Gamecontroller gameController;

 void Start()
 {
     GameObject gameControllerObject = GameObject.FindWithTag ("Gamecontroller");
     if (gameControllerObject != null) 
     {
         gameController = gameControllerObject.GetComponent<Gamecontroller> ();
     }
     if (gameController == null) 
     {
         Debug.Log ("Cannot find 'Gamecontroller'script");
     }
 }
 void OnTriggerEnter (Collider other)
 {
     if (other.tag == "Boundary")
     {
         return;
     }
     Instantiate (explosion, transform.position, transform.rotation);
     if (other.tag == "Player") {
         Instantiate (playerExplosion, other.transform.position, other.transform.rotation);
     }
     gameController.AddScore(scoreValue);
     Destroy (other.gameObject);
     Destroy (gameObject);
 }

}

Gamecontroller Script is..

using UnityEngine; using System.Collections;

public class Gamecontroller : MonoBehaviour { public GameObject hazard; public Vector3 spawnValues; public int hazardCount; public float spawnWait; public float startWait; public float waveWait;

 public GUIText scoreText;
 private int score;


 void Start()
 {
     score = 0;
     UpdateScore ();
     StartCoroutine(SpawnWaves());
 }

 IEnumerator SpawnWaves()
 {
     yield return new WaitForSeconds(startWait);
     while (true)
     {
         for(int i=0;i<hazardCount;i++)
         {
                 Vector3 spawnPosition = new Vector3 (Random.Range (-spawnValues.x, spawnValues.x), spawnValues.y, spawnValues.z);
                 Quaternion spawnRotation = Quaternion.identity;
                 Instantiate (hazard, spawnPosition, spawnRotation);
                 yield return new WaitForSeconds(spawnWait);
         }
         yield return new WaitForSeconds(waveWait);
     }
 }
 public void AddScore (int newScoreValue)
 {
     score += newScoreValue;
     UpdateScore ();
 }

 void UpdateScore()
 {
     scoreText.text = "Score: " + score;
 }

PLease anyone help me...

Thank you..