KML - Unsupported feature: kml error on Cesium 1.29

I have been working on loading kml files into the Cesium globe. The kml data source and cesium server are running on the same host. I am getting a "KML - Unsupported feature: kml" error whenever I render my app.
It works just fine on GE though.
It also works fine when I load the sample kml files from Cesium

Am I missing something here?

***********My Code************************************************

function startup(Cesium) {
    'use strict';


Cesium.BingMapsApi.defaultKey =XXXXX;
var viewer = new Cesium.Viewer('cesiumContainer');
viewer.infoBox.frame.sandbox = "allow-same-origin allow-top-navigation allow-pointer-lock allow-popups allow-forms allow-scripts";
var options = {
    camera :,
    canvas : viewer.scene.canvas

    text : 'KML - xGDS path',
    onselect : function() {;
        viewer.dataSources.add(Cesium.KmlDataSource.load('../../SampleData/kml/xgds.kml', options));
} ], 'toolbar');

Sandcastle.reset = function() {
    viewer.clock.clockRange = Cesium.ClockRange.UNBOUNDED;
    viewer.clock.clockStep = Cesium.ClockStep.SYSTEM_CLOCK;
if (typeof Cesium !== "undefined") {
} else if (typeof require === "function") {
    require(["Cesium"], startup);


While Cesium has pretty good KML support, we are missing support for certain features.

It sounds like your KML file might have a feature that we don’t support.

You can see a checklist of features we support here: