I am getting this and the stack trace does not offer any help as to what exactly the issue is or more importantly, WHERE...
Object reference not set to an instance of an object
UnityEngine.Debug:LogError(Object)
EventDelegate:Execute(List`1) (at Assets/NGUI/Scripts/Internal/EventDelegate.cs:623)
UIButton:OnClick() (at Assets/NGUI/Scripts/Interaction/UIButton.cs:248)
UnityEngine.GameObject:SendMessage(String, Object, SendMessageOptions)
UICamera:Notify(GameObject, String, Object) (at Assets/NGUI/Scripts/UI/UICamera.cs:1044)
UICamera:ProcessTouch(Boolean, Boolean) (at Assets/NGUI/Scripts/UI/UICamera.cs:1771)
UICamera:ProcessMouse() (at Assets/NGUI/Scripts/UI/UICamera.cs:1366)
UICamera:ProcessTouches() (at Assets/NGUI/Scripts/UI/UICamera.cs:1438)
UICamera:Update() (at Assets/NGUI/Scripts/UI/UICamera.cs:1185)