I get the error below in Unity and I cannot open any prefabs

Questions & Answers
1

Error while changing Stage:

System.NullReferenceException: Object reference not set to an instance of an object
  at UnityEditor.SceneManagement.StageHandle.FindComponentsOfType[T] () [0x000ad] in <1899c5bd2a6d466081cd705bee01d689>:0 
  at E7.NotchSolution.Editor.NotchSimulator.UpdateSimulatorTargets () [0x0008d] in C:\hitmatch\Assets\NotchSolution\Editor\Simulator\NotchSimulator.cs:299 
  at E7.NotchSolution.Editor.NotchSimulator+<>c.<EnsureCanvasAndEventSetup>b__30_0 (UnityEditor.SceneManagement.PrefabStage ps) [0x0003c] in C:\hitmatch\Assets\NotchSolution\Editor\Simulator\NotchSimulator.cs:523 
  at (wrapper delegate-invoke) System.Action`1[UnityEditor.SceneManagement.PrefabStage].invoke_void_T(UnityEditor.SceneManagement.PrefabStage)
  at UnityEditor.SceneManagement.PrefabStage.OpenStage () [0x00054] in <1899c5bd2a6d466081cd705bee01d689>:0 
  at UnityEditor.SceneManagement.PrefabStage.OnOpenStage () [0x0001e] in <1899c5bd2a6d466081cd705bee01d689>:0 
  at UnityEditor.SceneManagement.StageNavigationManager.SwitchToStage (UnityEditor.SceneManagement.Stage stage, System.Boolean setAsFirstItemAfterMainStage, UnityEditor.SceneManagement.StageNavigationManager+Analytics+ChangeType changeTypeAnalytics) [0x0014b] in <1899c5bd2a6d466081cd705bee01d689>:0 
UnityEngine.GUIUtility:ProcessEvent (int,intptr,bool&)
2

This error is caused by some kind of editor script, not the Editor itself. If this is part of a team project then contact your programmer and let him know the details of this issue.