Error: The root GameObject of the opened prefab... moved out of Prefab Stage...

After updgrading a project to 2018.4.2 & new prefabs. Many of the generated prefabs do not opene and show "Exiting Prefab Mode" dialog with "Error: The root GameObject of the opened Prefab has been moved out of the Prefab Stage scene by a script."

what is this about?!

Edit: old NGUI components are just not compatible with the prefab system - I need an NGUI update...
Fixed in newer NGUI - update in your current Unity, then update Unity version

 

I'm getting the same error, preventing me from editing the prefabs. Does anyone know how to fix this?

 

The answer is right in the first post you replied to.

 

For anyone interested: I wanted to change prefabs hierarchy if Application.IsEditor in Awake method. Since it depended on other objects, the Awake method probably failed when opening in Prefab Editor so long story short this helped me:

Before:

Code (CSharp):

1.  
2.     private void Awake()
3.     {
4.  
5.         if (Application.isEditor)
6.         {
7.                 world = GameObject.Find("World").GetComponent<WorldBehaviour>();
8.                 var unitWrapper = GameObject.Find("Units");
9.                 transform.parent = unitWrapper.transform;
10.             }
11.  
12.     }
13.  

After:

Code (CSharp):

1.  
2.     private void Awake()
3.     {
4.  
5.         if (Application.isEditor)
6.         {
7.             if (PrefabStageUtility.GetCurrentPrefabStage() == null)
8.             {
9.                 world = GameObject.Find("World").GetComponent<WorldBehaviour>();
10.                 var unitWrapper = GameObject.Find("Units");
11.                 transform.parent = unitWrapper.transform;
12.             }
13.  
14.         }
15.     }
16.