Android : Error in Assets folder while running Cordova Android App (plugin)

I'm developing a cordova android app and I'm getting an error while using a calendar plugin from github https://github.com/EddyVerbruggen/Calendar-PhoneGap-Plugin

the error is:

.....................................

my html file for including JSs

<script type=="text/javascript" src="cordova.js"></script>
<script type=="text/javascript" src="cordova_plugins.js"></script>
<script type=="text/javascript" src="JS/Calendar.js"></script>
<script src="JS/fncs.js"></script>

my fncs.js file is:

var startDate = new Date(2014,8,24,0,0,0,0,0);
var endDate = new Date(2014,8,27,0,0,0,0,0);
var title = "My nice event";
var location = "Home";
var notes = "Some notes about this event.";
var success = function(message) { document.getElementById("developers").innerHTML = "success";};
var error = function(message) { document.getElementById("developers").innerHTML = "failed";};
window.plugins.calendar.createCalendar(calendarName,success,error);

and here's my file structure:

JS folder >>

any help would be greatly appreciated .. thanks !