ExtJS 4: Uncaught Ext.Error: Ext.Loader is not enabled, so dependencies cannot be resolved dynamically. Missing required class:

if you get the error:

Uncaught Ext.Error: Ext.Loader is not enabled, so dependencies cannot be resolved dynamically. Missing required class: SIBismark.view.Viewport


Add the following line at the beginning of your js file

Ext.Loader.setConfig({enabled:true});


In Example in the app.js :



Ext.Loader.setConfig({enabled:true});
Ext.application({
    name: 'SI'
    ,requires:['SI.view.Viewport']
    ,autoCreateViewport: true
    ,launch: function() {        
        // This is fired as soon as the page is ready
    }
}); 


Reference:
http://www.sencha.com/learn/architecting-your-app-in-ext-js-4-part-3/