I tried, but same problem...

== Edit ==
The problem is happened to the static function "GetWorldCorners" in NGUITools.cs
Inside, when I choose perspective camera, it calls the "ViewportToWorldPoint" of delivered camera.
I've check basic parameters of that camera, all of them seems to be correct.
But when I try to use "ViewportToWorldPoint" and "WorldToViewportPiont" at this moment, these two method are broken!
I guess the inner variables are not fully initialized at that moment...
It only happened when I just start the editor.