No fullscreen possible

[My Games]

Hi. Am I missing something?

function OnStart()
{
    lay=app.CreateLayout("Linear", "Vertical,VCenter,FillXY");
    lay.SetBackground('/Sys/Img/GreenBack.jpg');
   
    spn=app.CreateSpinner("Default,Normal,Full,Game");
    spn.SetOnChange(SetScreenMode);
    lay.AddChild(spn);

    app.AddLayout(lay);
}

function SetScreenMode(mode)
{
    app.SetScreenMode(mode);
}