Level dont loaded, after enter a Trigger BoxCollider

Hello,
i want, that the game loads the next level, when my player enter a Triggerbox. But it doesnt work. When i make a button for load the next level it works? The player has the right tag. I have no idea. The script is attached to the box collider of the levelend.

My code:

using UnityEngine;
using System.Collections;

public class LoadNextLevel : MonoBehaviour {
	public string levelName ="";
	public string tag = "";

	// Use this for initialization
	void Start () 
	{
	
	}
	
	// Update is called once per frame
	void Update () 
	{
	
	}
	
	
	void OnTrigerEnter(Collider other)
	{
		if(other.gameObject.tag == tag)
		{
			Application.LoadLevel(levelName);
			Debug.Log("NextLevel");
		}
	}
	
	void OnGUI()
	{
		if(GUI.Button(new Rect(300,300,100,100),"NextLvl"))
		{
		
			Application.LoadLevel(levelName);
		}
	}
}

It should be ‘OnTriggerEnter()’ with two ‘g’.