null reference exception when creating a basic AI

[colpolstudios]

I am following along with the and the and i'm using the stealth kill scene as my testing area.

When I hit play unity displays this msg:

NullReferenceException: Object reference not set to an instance of an object
UnityEditor.GameObjectInspector.ClearPreviewCache () (at C:/buildslave/unity/build/Editor/Mono/Inspector/GameObjectInspector.cs:211)
UnityEditor.GameObjectInspector.OnDisable () (at C:/buildslave/unity/build/Editor/Mono/Inspector/GameObjectInspector.cs:199)

The AI goes to each way point.

Help please