JS CS3 Fastest way to create a group

Question

I have a selection of about 1050 elements and to create a group I'm using:
var myNewGroup = new Array;
for (i=app.selection.length-1; i>=0; i--) {
    myNewGroup.push (app.selection[i]);
  var myGroup = app.activeDocument.groups.add(myNewGroup);
This works but it's very slow. I have tried the following:
var myNewGroup = app.selection;
var myGroup = app.activeDocument.groups.add(myNewGroup);
The app.selection approach gives me an Invalid parameter error. What I don't understand is that the working code creates an array and adds each element to the array then a group is created from that array.
With the second approach app.selection is an array so why does this group?

Answer 1

Thanks again Kris,
The document I'm trying this on is supplied not created by me so I should of run a test on a doc a created first, so I did. I made a new A4 doc and place a number of text elements on the page then selected them and ran the script again. Sure enough the selection became a group.
So I went back to the supplied doc and selected a couple of the frame and check under the Object menu , Content and to my surprise the options Graphic, Text, and Unassigned were all grayed out (could not select any).
Yet when I ran:
$.write(app.selection[1].constructor.name+"\n");
the console returns TextFrame and for
$.write(app.selection[1].contentType+"\n");
the console returns 1952412773 (TEXT_TYPE).
So there seems to be an issue with the file not the script. Thanks for you help Kris much appreciated.