programming problem

Unity Engine
1 
#pragma strict

var ScoreUI : UI.Text;
var ScoreInt : int = 0;
var Score2Int : int = 0;

var Ball : GameObject;
var BallTransform : Transform;
var BallSpawn : Transform;

function Start () {
    BallTransform = GameObject.FindGameObjectsWithTag("Ball");
}

function Update () {
    ScoreUI.text = ("Home "+ ScoreInt+" - "+Score2Int+" Away");
}

function OnTriggerEnter (other : Collider) {
    if (other.tag == "Ball")
    {
        ScoreInt += 1;
        BallTransform.transform.position = BallSpawn.position;
        ScoreUI.text = ("Home "+ ScoreInt+" - "+Score2Int+" Away");
    }
}

I get the error “Cannot convert 'unityengine.GameObject[ ]'to 'unityengine.Transform”,
can someone give me the exact code that works?

2 
BallTransform = GameObject.FindGameObjectsWithTag("Ball");

FindGameObjectsWithTag returns a GameObject, however your variable is of type Transform. Also note that your are using FindGameObjectsWithTag which returns multiple instances in an array if found. So your code should look like this:

BallTransform = GameObject.FindGameObjectsWithTag("Ball")[0].transform;

Note that this is still not error prone as you should probably check if any objects were found at all.

3 
function Start () {
    BallTransform = GameObject.FindGameObjectsWithTag("Ball").transform;
}