transform.postion assign attempt error

I’m getting a really weird error that I can’t figure out. There error is:
transform.position assign attempt for ‘asteroidPrefab(Clone)’ is not valid. Input position is {3.874069, 3.855292, -Infinity}, UnityEngine.Transform.Translate(Single, Single, Single, Transform)

I have an AsteroidManager script that instantiates an asteroid prefab at one of four spawn points (empty game object). Now to be clear everything works perfectly. BUT recently I decided to reposition the spawn points slightly from on the z-axis and now I get this error. They started at 0 on the z-axis but if I move them in any positive or negative direction on the z-axis I get this error.

In case you want to see the scripts:

Here is the AsteroidManager script:

using UnityEngine;
using System.Collections;
using System.Collections.Generic;

public class AsteroidManager : MonoBehaviour {

    public GameManager gameManager;

    public GameObject asteroid;
    public List<GameObject> asteroidSpawn = new List<GameObject>();

    private int index;

    // Use this for initialization
    void Start ()
    {
        InvokeRepeating ("spawn", 4f, 4f);
    }
   
    // Update is called once per frame
    void Update ()
    {
   
    }

    void spawn ()
    {
        if (gameManager.gameOver == false)
        {
            index = Random.Range (0, asteroidSpawn.Count);
            Instantiate (asteroid, asteroidSpawn [index].transform.position, Quaternion.identity);
        }
    }
}

and here is the AsteroidController script:

using UnityEngine;
using System.Collections;

public class AsteroidController : MonoBehaviour {

    public GameManager gameManager;

    private float xSpeed = -3f;
    private float ySpeed = -3f;

    // Use this for initialization
    void Start ()
    {
        if (transform.position.x < 10)
        {
            xSpeed *= -1;
        }
    }
   
    // Update is called once per frame
    void Update ()
    {
        transform.Translate (xSpeed * Time.deltaTime, ySpeed * Time.deltaTime, transform.position.z, Camera.main.transform);
    }

    void OnTriggerEnter(Collider other)
    {
        if (other.tag == "Player")
        {
            Destroy (other.gameObject);
            Destroy (gameObject);
            GameManager.lives--;
            if (GameManager.lives > 0)
            {
                gameManager.respawnPlayer ();
            }
        }
    }
}

Could it be this line in my AsteroidController script causing problems?

transform.Translate (xSpeed * Time.deltaTime, ySpeed * Time.deltaTime, transform.position.z, Camera.main.transform);

When I comment it out I don’t get the error