Does "documentPreferences" still work?

Hello There.

I am trying the following script from the Adobe CS6 Scripting Tutorial:

try{

    myFont = app.fonts.item("Arial");

}

catch (myError){};

var myDocument = app.documents.item(0);

with(myDocument){

    var myPage = pages.item(0);

    var myBounds = myGetBounds(myPage,myDocument);

    with(myDocument.pages.item(0)){

    //Get a reference to the text frame.

    var myTextFrame = textFrames.item(0);

    //Change the size of the text frame.

    myTextFrame.geometricBounds = myBounds;

    var myParagraph = myTextFrame.paragraphs.item(0);

    myParagraph.appliedFont = myFont;

    myParagraph.justification = Justification.centerAlign;

    myParagraph.pointSize = 48;

    }

}

//myGetBounds is a function that returns the bounds

//of the "live area" of a page.

function myGetBounds(myDocument, myPage){

// line 28:

var myPageWidth = myDocument.documentPreferences.pageWidth;

var myPageHeight = myDocument.documentPreferences.pageHeight

if(myPage.side == PageSideOptions.leftHand){

var myX2 = myPage.marginPreferences.left;

var myX1 = myPage.marginPreferences.right;

}

else{

var myX1 = myPage.marginPreferences.left;

var myX2 = myPage.marginPreferences.right;

}

var myY1 = myPage.marginPreferences.top;

var myX2 = myPageWidth - myX2;

var myY2 = myPageHeight - myPage.marginPreferences.bottom;

return [myY1, myX1, myY2, myX2];

}

When I run it from the InDesign Scripts panel, I get the following:

Whats wrong?

Any help would be greatly appreciated.