Unity3d Script does not work anymore

I was working on a simple tank game. When the script I was using before suddenly stop working. I keep receiving the NullReferenceException: Object reference not set to an instance of an object error. I searched many questions online but none of them are similar to mine. The game object component that the unity engine claims is null is the parent of the script with the error. Moreover the script being referenced is what controls my game object which it does fine. Everything worked fine until I restarted my computer. I have gone over my script over and over and nothing have been changed but I keep getting the error. Here is the script with the error:

private GameObject i; 

// Use this for initialization
void Awake () {
    i = GameObject.FindGameObjectWithTag("WallBoy");
}

void Start () {
    i = GameObject.FindGameObjectWithTag("WallBoy");
}

void OnTriggerEnter(Collider other)
{
    if (other.gameObject.CompareTag ("Walls")) {
        i.GetComponent<TW>().x += 1;
    }
}
}

Broken Tags, just use an other tag that will solve it. Somehow updates seems to break stuff.