I was developing a game in Unity Basic but recently purchased Unity iPhone Basic to release the game on the iPad. Everything seems to look ok, except I am having a few weird script errors.

One: Operator '-' cannot be used with a left hand side of type 'Object' and a right hand side of type 'Object'.

var balls = GameObject.FindGameObjectsWithTag("Ball");

    var zs = new Array();
    var ys = new Array();


    for(var i = 0; i < balls.length; i++){
        zs[i] = balls[i].transform.position.z;
        ys[i] = balls[i].transform.position.y;
    }


    ys.Sort();
    zs.Sort();


    var zdiff = zs[zs.length-1] - zs[0]; // ERRORS HAPPEN HERE
    var ydiff = ys[ys.length-1] - ys[0]; // ERRORS HAPPEN HERE

What is wrong with the code? It works perfectly in both Windows and Mac Unity Basic... Are there any huge differences that I should know of between Unity iPhone and Desktop when scripting?