issue with adding an icon to a button

I have created a trusted function (code below), when I call this function the button gets created on the page however this button is just a blank box, how do I get an image to show in the created button.  I am running this in Adobe Reader XI, which I believe should allow this functionality, if not can anyone explain how I am able to add an image to a pdf using javascript. 

app.addToolButton({cName:"TestButton", cExec:"CreateMyButton('NextButton', this.pageNum)", cLabel:"Test Button", cTooltext:"Test_Button"});

var CreateMyButton = app.trustedFunction(function(cName, nPage)

{

  app.beginPriv();

  // Acquire the crop box (visible area) for the current page

  var pgRect = this.getPageBox("Crop", nPage);

  // Build Button Rectangle in lower left corner of page

  var fldRect = []; fldRect [0] = pgRect[0] + 36;

  // 1/2 inch from left side

  fldRect [1] = pgRect[0] + 56;

  // 20 points high

  fldRect [2] = pgRect[0] + 172;

  // 1/2 inch wide

  fldRect [3] = pgRect[0] + 136;

  // 1/2 inch from bottom

  // Create Button on page

  var oFld = this.addField( cName , "button", nPage, fldRect);

  // Setup Button's Properties

  if(oFld != null) {

  //oFld.buttonSetCaption("Next");

  oFld.buttonPosition = position.iconOnly;

  oFld.buttonImportIcon("/fileserver/folder/folder2/iconimage.pdf");

  oFld.borderStyle = border.b;

  // Beveled edges

  oFld.strokeColor = color.blue;

  // Border Color

  oFld.textColor = color.black; oFld.lineWidth = 1;

  // Thin Border

  oFld.setAction("MouseUp", "this.pageNum++");

  // Navigation

  }

  return oFld;

  app.endPriv();

});