NGUI UI inactive

Hello. I have a problem : I bought NGUI, and when loading a Tutorial scene and Playing it, i’m trying to push a button, or slide a slider, check a checkbox, but it is still inactive and i can’t uncheck, move the slider, drag the window… I can’t do anything ?!

Do you know what should I do ?

[752-Sans+titre.jpg|752]

Go to this. And watch the video before using it.