Unity crashes whenever i activate my script... ,I have a script that crashes whenever i activate it....

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

public class OilRigSpawnGen : MonoBehaviour {

//public List<GameObject> units = new List<GameObject>();

public GameObject waterTiles;

void Update()
{
    if (Input.GetKeyDown(KeyCode.G))
    {
        for (int x = 0; x < 3; x++)
        {
            for (int z = 0; z < 3; z++)
            {

                this.gameObject.transform.position = new Vector3(gameObject.transform.position.x,0, gameObject.transform.position.z);
                GameObject tileClone = Instantiate(waterTiles.gameObject, new Vector3(transform.position.x - (55 * x), 0, transform.position.z - (55 * z)), Quaternion.identity) as GameObject;

                //units.Add(tileClone.gameObject);
            }
        }
    }
}

}

I tested your code and it doesnt crash. Maybe you are spawning too complex a model. I tested with cylinders and it makes a very widely spaced out grid of 9.