Application.LoadLevelAsync Will only work once per game

Im using Application.LoadLevelAsync to show a loading scene while a large scene is loaded, the problem is that it only works once, the second time I try to load another level from the main menu it stays in the loading scene and never loads.

I have also tried it without the loading scene and I get the same result. What can I do?

This is my entire coroutine

Code (csharp):

1.     public IEnumerator LoadLevel(string level, int checkpoint){
2.         //currentLevel=level;
3.         if (isLoading) return;
4.         Application.LoadLevel("loading");
5.         yield return new WaitForSeconds(1.5f);
6.         currentCheckpoint=checkpoint;
7.         AsyncOperation ao=Application.LoadLevelAsync(level);
8.         isLoading=true;
9.         while(!ao.isDone)
10.         {
11.             loadProgress = ao.progress;
12.             Debug.Log("Load progress "+  loadProgress);
13.             yield return 0;
14.         }      
15.         isLoading=false;
16.         AfterLevelLoaded();
17.     }
18.  

 

either try just doing

yield return ao; (will wait for the level to load)

or not yield return 0 but instead

yield return null; (will wait for next frame)

 

Also make sure you've got this script using DontDestroyOnLoad