NullReferenceException: Object reference not set to an instance of an object
KeepTrackOfOpenWindow.OnClick () (at Assets/Khoda/Scripts/Q&A/KeepTrackOfOpenWindow.cs:12)
UnityEngine.GameObject:SendMessage(String, Object, SendMessageOptions)
UICamera:Notify(GameObject, String, Object) (at Assets/NGUI/Scripts/UI/UICamera.cs:1065)
UICamera:ProcessTouch(Boolean, Boolean) (at Assets/NGUI/Scripts/UI/UICamera.cs:1808)
UICamera:ProcessMouse() (at Assets/NGUI/Scripts/UI/UICamera.cs:1402)
UICamera:ProcessTouches() (at Assets/NGUI/Scripts/UI/UICamera.cs:1474)
UICamera:Update() (at Assets/NGUI/Scripts/UI/UICamera.cs:1221)