index error

I am getting the same error here, not sure how to tell which line it is at

 using System;
 using System.Collections.Generic;
 using UnityEngine;
 using Random = UnityEngine.Random;
 
 
 public class BoardManager : MonoBehaviour {
     public class Count{
         
         public int minimum;
         public int maximum;
 
         public Count(int min,int max){
             minimum= min;
             maximum = max;
         
         }
     }
 
     public int columns = 8;
     public int rows = 8;
     public Count wallCount =new Count (5,9);
     public Count foodCount = new Count (1, 5);
     public GameObject exit;
     public GameObject[] floorTiles;
     public GameObject[] wallTiles;
     public GameObject[] foodTiles;
     public GameObject[] enemyTiles;
     public GameObject[] outerWallTiles;
 
     private Transform boardHolder;
     private List <Vector3> gridPositions = new List<Vector3>();
 
     void InitialiseList(){
         gridPositions.Clear();
         for(int  x =1;x < columns -1; x++){
             for(int y=1; y< rows -1; y++){
                 gridPositions.Add(new Vector3(x,y,0f));
             }
         }
 
     }
 
     void BoardSetup (){
         boardHolder = new GameObject ("Board").transform;
         for(int  x =-1;x < columns + 1; x++){
             for(int y=-1; y< rows +1; y++){
                 GameObject toInstantiate = floorTiles[Random.Range(0, floorTiles.Length)];
                 if (x == -1 || x == columns || y == -1 || y == rows) {
                     toInstantiate = outerWallTiles[Random.Range(0, outerWallTiles.Length )];
 
                 GameObject instance = Instantiate(toInstantiate, new Vector3(x, y, 0f), Quaternion.identity) as GameObject;
 
                 instance.transform.SetParent(boardHolder);
                 }
             }
         }
 
     }
 
     Vector3 RandomPosition(){
         int randomIndex = Random.Range(0, gridPositions.Count);
         Vector3 randomPosition = gridPositions[randomIndex];
         gridPositions.RemoveAt(randomIndex);
         return RandomPosition();
 
     }
 
     void LayoutObjectAtRandom(GameObject[] tileArray, int minimum, int maximum){
         int objectCount = Random.Range (minimum, maximum + 1);
 
         for (int i = 0; i < objectCount; i++) {
             Vector3 randomPosition = RandomPosition();
             GameObject tileChoice = tileArray[Random.Range (0, tileArray.Length)];
             Instantiate (tileChoice, randomPosition, Quaternion.identity);
         }
     }
 
 
     public void SetupScene (int level){
         BoardSetup ();
         InitialiseList ();
         LayoutObjectAtRandom (wallTiles, wallCount.minimum,wallCount.maximum);
         LayoutObjectAtRandom (foodTiles, foodCount.minimum, foodCount.maximum);
         int enemyCount = (int)Math.Log (level, 2f);
         LayoutObjectAtRandom(enemyTiles, enemyCount, enemyCount);
         Instantiate (exit, new Vector3(columns -1,rows -1, 0f), Quaternion.identity);
 
     }
     // Use this for initialization
     void Start () {
         
     }
     
     // Update is called once per frame
     void Update () {
         
     }
 }