Physics.CheckSphere always give false (Unity3D) - unity3d

Question

I'm trying to create objects that mark the cell that I can visit. I mark them with red square:
My code for creating objects:
using UnityEngine;
using System.Collections;
using System;
public class SpawnCheck : MonoBehaviour {
public GameObject checkObject;
public bool canSpawnCheck = true;
Vector2 boxSize;
public GameObject spawnedObject;
// Use this for initialization
void Start () {
Debug.Log("Into spawn check");
}
void OnTriggerEnter2D(Collider2D other) {
Debug.Log("Enter trigger collision");
canSpawnCheck = false;
if (other.gameObject.tag == "Target") {
Debug.Log ("Found Target");
}
if (other.gameObject.tag == "Wall") {
canSpawnCheck = false;
}
if (other.gameObject.tag == "Check") {
canSpawnCheck = false;
}
}
void OnTriggerExit2D(Collider2D other) {
Debug.Log("Exit trigger collision");
canSpawnCheck = true;
}
// Update is called once per frame
void Update () {
Debug.Log ("canSpawnCheck " + canSpawnCheck);
if (canSpawnCheck == true) {
Vector3 currentPosition = this.gameObject.transform.position;
Vector3 spawnPos = new Vector3 (Mathf.Round (currentPosition.x), Mathf.Round (currentPosition.y),0);
Debug.Log ("Physics.CheckSphere " + Physics.CheckSphere (spawnPos, 5));
if (!Physics.CheckSphere(spawnPos,5)) {
spawnedObject = (GameObject)Instantiate (checkObject, spawnPos, Quaternion.identity);
this.gameObject.GetComponentInParent<AILerp> ().possibleTargets.Add (spawnedObject);
}
}
}
}
My problem: as Physics.CheckSphere(spawnPos,5) always return false my code spawns too many red squares and spawn them upon each other. I want red squares to be created only once and never created on walls (white squares).

Answer 1

Your Check(Clone) GameObject has Box Collider 2D attached to it. Therefore every physics function you must use should be Physics2D.something not Physics.something. Notice the keyword there "2D".
If you use just Box Collider without the 2D in it, then you can use Physics.something. So, Physics.CheckSphere cannot be used with a 2D collider.
Check(Clone) is a SpriteRenderer, 2D Collider is appropriate. You just need to use one of the Physics2D overlap functions such Physics2D.OverlapBox, Physics2D.OverlapArea or Physics2D.OverlapCircle. Which ever one you prefer.