Scene is not Loading.

There are 9 Scenes all are Added in SceneManager but it kept saying.

"Scene ‘SceneName’ couldn’t be loaded because it has not been added to the build settings or the AssetBundle has not been loaded.
To add a scene to the build settings use the menu File->Build Settings…
UnityEngine.SceneManagement.SceneManager:LoadSceneAsync(String, LoadSceneMode)
MoreMountains.CorgiEngine.c__Iterator0:MoveNext() (at Assets/CorgiEngine/Common/Scripts/Managers/LoadingSceneManager.cs:88)
UnityEngine.MonoBehaviour:StartCoroutine(IEnumerator)
MoreMountains.CorgiEngine.LoadingSceneManager:Start() (at Assets/CorgiEngine/Common/Scripts/Managers/LoadingSceneManager.cs:67)

"

I have already added the scene in scene manager. but it keeps showing this error. i have tried so much.Please help me to sort out the problem.
Here is my “LoadingSceneManager” script
using UnityEngine;
using UnityEngine.UI;
using System.Collections;
using System.Collections.Generic;
using MoreMountains.Tools;
using UnityEngine.SceneManagement;

namespace MoreMountains.CorgiEngine
{	
	/// <summary>
	/// A class to load scenes using a loading screen instead of just the default API
	/// </summary>
	public class LoadingSceneManager : MonoBehaviour 
	{
		[Header("Binding")]
		/// The name of the scene to load while the actual target scene is loading (usually a loading screen)
		public static string LoadingScreenSceneName="LoadingScreen";

		[Header("GameObjects")]
		/// the text object where you want the loading message to be displayed
		public Text LoadingText;
		/// the canvas group containing the progress bar
		public CanvasGroup LoadingProgressBar;
		/// the canvas group containing the animation
		public CanvasGroup LoadingAnimation;
		/// the canvas group containing the animation to play when loading is complete
		public CanvasGroup LoadingCompleteAnimation;

		[Header("Time")]
		/// the duration (in seconds) of the initial fade in
		public float StartFadeDuration=0.2f;
		/// the speed of the progress bar
		public float ProgressBarSpeed=2f;
		/// the duration (in seconds) of the load complete fade out
		public float ExitFadeDuration=0.2f;
		/// the delay (in seconds) before leaving the scene when complete
		public float LoadCompleteDelay=0.5f;

		protected AsyncOperation _asyncOperation;
		protected static string _sceneToLoad = "";
		protected float _fadeDuration = 0.5f;
		protected float _fillTarget=0f;
		protected string _loadingTextValue;

		/// <summary>
		/// Call this static method to load a scene from anywhere
		/// </summary>
		/// <param name="sceneToLoad">Level name.</param>
		public static void LoadScene(string sceneToLoad) 
		{		
			_sceneToLoad = sceneToLoad;					
			Application.backgroundLoadingPriority = ThreadPriority.High;
			if (LoadingScreenSceneName!=null)
			{
				SceneManager.LoadScene(LoadingScreenSceneName);
			}
		}

		/// <summary>
		/// On Start(), we start loading the new level asynchronously
		/// </summary>
		protected virtual void Start() 
		{
			_loadingTextValue=LoadingText.text;
			if (_sceneToLoad != "")
			{
				StartCoroutine(LoadAsynchronously());
			}
		}

		/// <summary>
		/// Every frame, we fill the bar smoothly according to loading progress
		/// </summary>
		protected virtual void Update()
		{
			LoadingProgressBar.GetComponent<Image>().fillAmount = MMMaths.Approach(LoadingProgressBar.GetComponent<Image>().fillAmount,_fillTarget,Time.deltaTime*ProgressBarSpeed);
		}

		/// <summary>
		/// Loads the scene to load asynchronously.
		/// </summary>
		protected virtual IEnumerator LoadAsynchronously() 
		{
			// we setup our various visual elements
			LoadingSetup();

			// we start loading the scene
			_asyncOperation = SceneManager.LoadSceneAsync(_sceneToLoad,LoadSceneMode.Single );
			_asyncOperation.allowSceneActivation = false;

			// while the scene loads, we assign its progress to a target that we'll use to fill the progress bar smoothly
			while (_asyncOperation.progress < 0.9f) 
			{
				_fillTarget = _asyncOperation.progress;
				yield return null;
			}
			// when the load is close to the end (it'll never reach it), we set it to 100%
			_fillTarget = 1f;

			// we wait for the bar to be visually filled to continue
			while (LoadingProgressBar.GetComponent<Image>().fillAmount != _fillTarget)
			{
				yield return null;
			}

			// the load is now complete, we replace the bar with the complete animation
			LoadingComplete();
			yield return new WaitForSeconds(LoadCompleteDelay);

			// we fade to black
			GUIManager.Instance.FaderOn(true,ExitFadeDuration);
			yield return new WaitForSeconds(ExitFadeDuration);

			// we switch to the new scene
			_asyncOperation.allowSceneActivation = true;
		}

		/// <summary>
		/// Sets up all visual elements, fades from black at the start
		/// </summary>
		protected virtual void LoadingSetup() 
		{
			GUIManager.Instance.Fader.gameObject.SetActive(true);
			GUIManager.Instance.Fader.GetComponent<Image>().color=new Color(0,0,0,1f);
			GUIManager.Instance.FaderOn(false,ExitFadeDuration);

			LoadingCompleteAnimation.alpha=0;
			LoadingProgressBar.GetComponent<Image>().fillAmount = 0f;
			LoadingText.text = _loadingTextValue;

		}

		/// <summary>
		/// Triggered when the actual loading is done, replaces the progress bar with the complete animation
		/// </summary>
		protected virtual void LoadingComplete() 
		{
			LoadingCompleteAnimation.gameObject.SetActive(true);
			StartCoroutine(MMFade.FadeCanvasGroup(LoadingProgressBar,0.1f,0f));
			StartCoroutine(MMFade.FadeCanvasGroup(LoadingAnimation,0.1f,0f));
			StartCoroutine(MMFade.FadeCanvasGroup(LoadingCompleteAnimation,0.1f,1f));

		}
	}
}

You have to add the scene to the File->Build Settings under the Scenes In Build section. If you have added the scene and still it is not loading then you have to check if, “LoadingScreenSceneName” is same as the scene added in build setting with case sensitivity.

@FarooqKhawaja

Same problem here… I checked and is the same name everywhere =/