While trying to use a filter in a grid, the following thing happened

the grid keeps on loading and following error comes

this.proxy is undefined

here is the code:

Code:
var filtersForAttrbuteGrid = new Ext.grid.GridFilters({
      filters:[
         {
          type: 'string', 
          dataIndex: 'AttributeName'
         },  
         {
          type: 'list',  
          dataIndex: 'DataType', 
          options: attrDataList 
        },
        { 
          type: 'list',  
          dataIndex: 'Range', 
          options: attrRangeList
        },
         {
          type: 'list',
          dataIndex: 'UseType',
          options : attrSectionorUseList 
        
        },
        {
          type: 'list', 
          dataIndex: 'ApplicableFor',
          options : attrApplicableList
        }
    ]});

var pagingBar = new Ext.PagingToolbar({
        id:'attr_pagingBar',
        pageSize: attr_PageSize,
        store: simpleStore,
        displayInfo: true,
        displayMsg: 'Displaying Attributes {0} - {1} of {2}',
        paramNames:{
                    start:'start',
                    limit:'pageSize',
                    sort:'sort',
                    dir:'dir'
                
                    },
            listeners:{
                        change : function(toolBar, event){

                            var startRowNum = (event.activePage - 1) * attr_PageSize;
                            //alert('startRowNum '+startRowNum);
                            renumberRows(simpleStore, startRowNum);

                        } 
                        /*
                        beforechange : function(pagingToolBar, event){
                            
                        //alert("Inside beforechange = "+event.start);
                        varstart = event.start;    
                        }*/
        },
        plugins : filtersForAttrbuteGrid,
        emptyMsg: "No Attribute to display"
    });


  var grid = new Ext.grid.GridPanel({
        id:att_grid_panel_id,
        ds: simpleStore,
        cm: cm,
         sm: new Ext.grid.RowSelectionModel({
                    singleSelect: true
                  
                }),
         stripeRows: true,
         viewConfig: {
             forceFit: true
         },
      
        layout:'fit',
        title: 'Attibute Editor',
        loadMask: {msg: 'Loading ...'},
        tbar : tBar,
          bbar : pagingBar,
        plugins : filtersForAttrbuteGrid
            
    });