Box Collider and AI

I am using a simple waypoint script that takes the AI around a small circle of 8 waypoints. The script works fine without any collision detection, but when I add a collider of sorts (Like a box collider) the script stops working. Here’s my script below: `#pragma strict

var grid : Transform;
var speed : float = 5.0;
var current : int;

function Start () {

}

function Update () {

if(current < grid.Length){

	//variables to determine movement
	var target : Vector3 = grid[current].position;
	var moveDirection : Vector3 = target - transform.position;
	var velocity = rigidbody.velocity;
	
	//if close to the waypoint, increase current
	if(moveDirection.magnitude < 1){
		current++;
	} else {
	
		velocity = moveDirection.normalized * speed;
	}
	
	//set the rigid body velocity to move
	rigidbody.velocity = velocity;

} else {
	current = 0;

`
Could anyone please help me so that I can run my AI script with a physics collider attached to my AI?

Do you use a rigidbody without a collider? A rigidbody always needs a collider, or where do you attach the BoxCollider? I guess your rigidbody just get stuck on another collider?

What exactly does “stops working” mean? Does it still move but too slow / the wrong way / …? Do you get errors? What exactly changed when you attached a collider.