I am upgrading a app. from extjs 3.2 to extjs 4

In this project I am fetching d data from database, I came across a problem

Uncaught Ext.Error: Ext.Loader is not enabled, so dependencies cannot be resolved dynamically. Missing required classes: Ext.ux.grid.FiltersFeature, Ext.ux.RowExpander, Ext.ux.PreviewPlugin

cant resolve it, plz post ur suggestions