Sencha Touch 2 Can't Parse Json data

Question

I'm very new to Sencha touch. I have to Load JSON data in a list.

My Panel.js

Ext.define('MyApp.view.MyPanel', {
    extend: 'Ext.Panel',

    requires: [
        'Ext.Toolbar',
        'Ext.dataview.List',
        'Ext.XTemplate'],

    config: {
        items: [{
            xtype: 'toolbar',
            docked: 'top',
            title: 'Test'
        }, {
            xtype: 'list',
            itemTpl: [
                '\'<tpl for="polls">\',',
                '                \'<div> {title}</div>\',',
                '                \'<div> {uri}</div>\',',
                '\'</tpl>\','],
            store: 'MyStore'
        }]
    }

});

MyModel.js

Ext.define('MyApp.model.MyModel', {
    extend: 'Ext.data.Model',

    requires: [
        'Ext.data.Field',
        'Ext.data.proxy.JsonP'],

    config: {
        fields: [{
            name: 'title'
        }, {
            name: 'uri'
        }]
    }
});

MyStore.js

Ext.define('MyApp.store.MyStore', {
    extend: 'Ext.data.Store',

    requires: [
        'MyApp.model.MyModel',
        'Ext.data.proxy.JsonP',
        'Ext.data.reader.Json'],

    config: {
        autoLoad: true,
        model: 'MyApp.model.MyModel',
        storeId: 'MyStore',
        proxy: {
            type: 'jsonp',
            url: 'my_web_site_url/polls',
            reader: {
                type: 'json',
                rootProperty: 'polls'
            }
        }
    }
});

The JSON FILE has the following format..

{
 "polls": [
  {
     "title": "how r u?", 
      "uri": "/polls/answer1"
   }
 ]
}

and my_web_site_url/polls/uri will give u the

{
  "choices": [
    {
      "choice": "fine", 
       "votes": 0
    }, 
    {
       "choice": "good", 
      "votes": 0
       }, 
    {
      "choice": "sad", 
      "votes": 0
    }
  ], 
  "title": "how r u?", 
  "uri": "/polls/answers1"
}

When I try 'Load Data' in the Sencha Architect it shows:

Unable to load the data Using the supplied Configuration open in Browser my_website_url/polls