GUI box problem?

I ran into a problem with making a GUI box that covers the entire screen. Here is my script-

 var tex : Texture;
 function OnGUI () 
 {
     GUI.DrawTexture(Rect(0,0,Screen.width,Screen.height), tex, ScaleMode.ScaleToFit, true, 10.0f);
 }

Seems simple, right? It's almost a carpon copy of what is on the Unity docs page for DrawTexture. This is the output...

https://drive.google.com/file/d/0B9moL9M0YnOtOHlwNW9zZnRZd00/view?usp=sharing

(Sorry for a drive link, computer wasn't cooperating)

A black band across the middle?

Maybe a U5 problem?