I had this same problem. Eventually, looking at the index.html in the Appframework Kitchen Sink, I found out that to make the error disappear you need the following script inside the app index.html:
var webRoot = "./";
$.ui.autoLaunch = false; //By default, it is set to true and you're app will run right away. We set it to false to show a splashscreen
/* This function runs when the body is loaded.*/
var init = function () {
$.ui.backButtonText = "Back";// We override the back button text to always say "Back"
window.setTimeout(function () {
$.ui.launch();
}, 1500);//We wait 1.5 seconds to call $.ui.launch after DOMContentLoaded fires
};
document.addEventListener("DOMContentLoaded", init, false);
$.ui.ready(function () {
//This function will get executed when $.ui.launch has completed
});
I don't know yet why this code is needed, but its use is also documented here.