problem in creating buttons for augmented reality app

i am trying to develope an AR app..for androiod and i just create the buttons, to gave some functionalities to my objects based on butttons using ONGUI after tracking the objects..but when i pressed buttons while running it shows the error like.........

UnassignedReferenceException: The variable Cube of ImageTargetTrackableEventHandler has not been assigned.
You probably need to assign the Cube variable of the ImageTargetTrackableEventHandler script in the inspector.
ImageTargetTrackableEventHandler.OnGUI () (at Assets/Scripts/ImageTargetTrackableEventHandler.cs:136)

 

There are a lot of error message in Unity, and some of them are cryptic and really unhelpful.

This is not one of them.... it tells you exactly what you need to do.

 

thank u for your reply, ya i made mistake in my inspector.............now i correted it