Unable to print using ArcGIS javascript under IE9

I am trying to print a web map using ArcGIS javascript 3.10 under IE9 but got RequestError: Unable to load /proxy?http://myserver:6080/arcgis/rest/services/Utilities/PrintingTools/GPServer/Export%20Web%20Map%20Task/execute status: 404. However, the same map printed without any problem for IE11, Chorme and Firefox. This seems to me is because of proxy error but only specific to IE9.

The codes as follow:

esriConfig.defaults.io.proxyUrl = "/proxy";
function createPrintDijit() {
  var layoutTemplate, templateNames, mapOnlyIndex, templates;
  var path = document.getElementById("path").value;
  var printTitle = document.getElementById("printTitle").value;
  var legendLayers = [];
  var legendLayer = new LegendLayer();
  legendLayer.layerId = "countryParks"
  legendLayers.push(legendLayer);
  legendLayer = new LegendLayer();
  legendLayer.layerId = "amphibianGridMap"
  legendLayers.push(legendLayer);
  var layouts = [{
    name: "Letter ANSI A Landscape",
    label: "Landscape (PDF)",
    format: "pdf",
    options: {
      legendLayers: legendLayers, // empty array means no legend
      scalebarUnit: "Kilometers",
      titleText: printTitle
    }
  }];
  var templates = arrayUtils.map(layouts, function (lo) {
    var t = new PrintTemplate();
    t.layout = lo.name;
    t.label = lo.label;
    t.format = lo.format;
    t.layoutOptions = lo.options;
    return t;
  });
  app.printer = new Print({
    map: app.map,
    templates: templates,
    url: "http://myserver/arcgis/rest/services/Utilities/PrintingTools/GPServer/Export%20Web%20Map%20Task"
  }, dom.byId("printButton"));
  app.printer.startup();
}