polymer 1.0 .. importing a catalog element with a custom element throws an error - polymer-1.0

Question

Had created and used my custom polymer element which is a table. Now, I want to use the check box element from their catalog in my table.
However, I keep getting this error when I reference the check box html file in my index page:
DuplicateDefinitionError: a type with name 'dom-module' is already
registered
This is how I have created my custom element:
<!-- Imports polymer -->
<link rel="import" href="polymer/polymer.html">
<script src="underscore-min.js"></script>
<!-- Defines element markup -->
<dom-module id="custom-table" >
<template>
<style>
ul {list-style-type:none; display:block}
ul li {display:inline; float:left; padding:20px; width:1.5em; border-bottom:1px solid #eee}
</style>
<h2>{{title}}</h2>
<table id="dataTable">
<thead id="tableHead"></thead>
<tbody id="tableBody"></tbody>
</table>
</template>
</dom-module>
<!-- Registers custom element -->
<script>
Polymer({
is: 'custom-table',
// Fires when an instance of the element is created
created: function() {
},
// Fires when the local DOM has been fully prepared
ready: function() {
var context= this;
this.pageNo=0;
this.totalPages=0;
// set the default paging size:
if(this.page== null|| this.page==undefined)
this.page=10;
// delegate the change selection handler to the table body
this.$.tableBody.addEventListener("click",function(e){
if(e.target && e.target.nodeName == "INPUT") ;
{
context.changeSelection(e.target);
}
});
},
// Fires when the element was inserted into the document
attached: function() {},
// Fires when the element was removed from the document
detached: function() {},
// Fires when an attribute was added, removed, or updated
attributeChanged: function(name, type) {
alert("changed");
},
loadData: function(columns,data){
this.data = data;
// add the selected property to the values
for(var i=0;i<this.data.length; i++) { this.data[i].Selected = false;}
this.filteredData=this.data;
this.columns = columns;
//initialize the filteredData
this.filteredData=data;
// calculate the total number of pages
this.totalPages= Math.ceil(data.length/this.page);
this.drawTableHeader();
_.defer(this.applyFilters,this);
_.defer(this.drawTableBody,this);
},
drawTableHeader:function(){
var columns = this.columns;
// load the header
var headTr = document.createElement('tr');
//add a blank header for the check box;
var th=document.createElement('th');
headTr.appendChild(th);
for(var i = 0; i<columns.length ;i++)
{
var td=document.createElement('th');
// if the column is sortable then add the event listener for sorting it
if(columns[i].Sortable)
{
td.addEventListener("click",function(){ this.sortBy(columns[i].Title); });
}
td.innerText = columns[i].Title;
headTr.appendChild(td);
}
this.$.tableHead.appendChild(headTr);
},
drawTableBody: function(context){
// this is a defered function
var context = context;
// get the number of items according to the current page number
var pageItems= context.filteredData.slice((context.page*context.pageNo),((context.page*context.pageNo)+context.page));
console.log(pageItems);
// print the page items
for(var i=0; i < pageItems.length; i++)
{
var currItem = pageItems[i];
var tr= document.createElement("tr");
// add the check box first
var checkbox= document.createElement("input");
checkbox.type="checkbox";
checkbox.checked=pageItems[i].Selected;
var ItemId = currItem.Id;
checkbox.setAttribute("data-ItemId",ItemId-1);
var td=document.createElement('td');
td.appendChild(checkbox);
tr.appendChild(td);
// for every column specified add a column to it
for(var j = 0; j< context.columns.length; j++)
{
var td=document.createElement("td");
td.innerText= pageItems[i][context.columns[j].Title];
tr.appendChild(td);
}
//append the row to the table;
context.$.tableBody.appendChild(tr);
} // end for i
},
applyFilters:function(context){
if(context.filter)
{
alert("filterApplied");
}
},
changeSelection:function(checkbox){
var ItemId = checkbox.getAttribute("data-ItemId");
this.data[ItemId].Selected= checkbox.checked;
console.log(this.data[ItemId]);
},
properties:{
title :String,
columns:Array,
data:Array,
page:Number,
filters:Object,
Selectable:Boolean
}
});
</script>
and here is what my index page looks like:
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title><my-repo></title>
<!-- Imports polyfill -->
<script src="webcomponents-lite.min.js"></script>
<!-- Imports custom element -->
<link rel="import" href="my-element.html">
<link rel="import" href="bower_components/paper-checkbox/paper-checkbox.html">
</head>
<body unresolved>
<!-- Runs custom element -->
<custom-table title="This is data table"></custom-table>
<script>
document.addEventListener("WebComponentsReady",function(){
var data = [{'Id':1,'firstName':'aman',age:25},{'Id':2,'firstName':'gupta',age:25}];
var cols = [{Title:'firstName',Sortable:true},{Title:'age',Sortable:false}];
var a = document.querySelector('my-element');
a.loadData(cols,data);
});
</script>
</body>
</html>
I've just started out with polymer and I'm not quite sure what's going on here..
Thank you in advance :)

Answer 1

I got what the problem is..
My custom element was referencing a different Polymer.html file.
Silly me :D

Answer 2

I'm using Polymer Starter Kit Yeoman generator on Windows and I had the same problem:
Error: DuplicateDefinitionError: a type with name 'dom-module' is already registered
This error is triggered in Firefox console. Chrome works fine.
The components created with the generator (example: yo polymer:el my-element) have this polymer.html import:
<link rel="import" href="..\..\bower_components/polymer/polymer.html">
The base path is described with "backslash".
In some custom polymer elements I created by myself, I imported polymer.html with:
<link rel="import" href="../../bower_components/polymer/polymer.html">
And I think this lead to a duplication of some kind. To solve the problem, I just changed all automatically created imports, using only forward slashes /.
Hope this helps someone.