Screen.currentResolution = Null?

Hi every one, I found this little issue (Unity 3.4.2):

var showOnOff : boolean;
var useScreen : boolean;
//
function OnGUI {
//
    if (!showOnOff) {
        if (GUI.Button(Rect(), "Title Screen")) {
            showOnOff = true;
        }
    }
    else {
        GUI.Box(Rect(0, 0, useScreen ? Screen.width : 640, useScreen ? Screen.height : 480), "This is the Title");
    }
}

When I try to draw a gui box using the screen size the debuger show this:

NullReferenceException: Object reference not set to an instance of an object
Boo.Lang.Runtime.RuntimeServices.CheckNumericPromotion (IConvertible convertible)
Boo.Lang.Runtime.RuntimeServices.CheckNumericPromotion (System.Object value)
Boo.Lang.Runtime.RuntimeServices.UnboxSingle (System.Object value)
Screen.OnGUI () (at Assets/Screen.js:11)

This is kind of weird because some time before I can use this type of function in my projects (Unity 3.3), even if I try to check the screen resolution using this:

Debug.Log (Screen.currentResolution);

The debuger show this:

Null

UnityEngine.Debug:Log(Object)

How can this be possible!, any help will be appreciated, thanks in advance.

Try putting ‘new’ in front of Rect, and Rect() needs 4 integer numbers listed there, right? I think the null you are seeing is from the Rect, not Screen