getPageBox() and jscript error

i'm using windows scripting host and jscript (not vbscript). i cannot read anything returned by getPageBox(). the array is always empty. in fact, i seem to have problems with all methods that return arrays, so solving this coding error should clear up my other problems as well. here's part of my code.

var avdoc = WScript.CreateObject("AcroExch.AVDoc");
avdoc.Open("c:\\temp\\a.pdf", "temp");
var ppdDoc = avdoc.GetPDDoc();
var oJS = ppdDoc.GetJSObject();
WScript.Echo(oJS.info.Title); //no problem here
var a = new Array(4);
a = oJS.getPageBox("Media"); //"Art", "Crop","Trim", etc all fail as well
WScript.Echo(a[0]); // no error produced, but no output
WScript.Echo(oJS.getPageBox("Media")[0]); //second try, and still no output