Grid empty afer reconfigure()

[Mooi]

I like to create a site with some Gridpanels wit some dummy stores.
At runtime the Gridpanel and Stores have to be filled with real data.

The code below works, except that after the 'reconfigure()' my grid is empy, however the headers are filled ok.
The store is filled correctly also.
What is wrong in my code?

I am using a test Complete Sencha from a few weeks ago.

        initStores: function() {
        MyApp.uid = 'jan';
        MyApp.pwd = '123';
        MyApp.domain = 'tspalm:8082' ;
        var storeId = 'PARTIJ_DETAIL';

        var sqlCommandId = 'PARTIJ';
        var sqlView = 'DETAIL';
        var store = Ext.getStore('Headers');
        store.getProxy().url = 'http://www.wmysite.com/callback.php?loginUsername=' + MyApp.uid + '&loginPassword=' + MyApp.pwd + '&loginIp=' + MyApp.domain + '&level=8&commandid=' + sqlCommandId + '&viewid=' + sqlView + '&params=';
        store.remove(store.getRange());
        store.load({
            scope : this,
            callback: function(records, operation, success) {
                if (success) {

                    console.log('Headers gelezen');
                    console.log(records);           
                    // initiate arrays
                    var fieldNames = [];
                    var modelFields = [];
                    var columnNames = [];


                    Ext.Array.each(records, function(prop) {
                        fieldNames.push(prop.data.cname);
                    });


                    Ext.Array.each(fieldNames, function(fldname){
                        modelFields.push({name: fldname, type: 'string'});
                    });            


                    Ext.Array.each(fieldNames, function(fldname){
                        columnNames.push({dataindex: fldname, 
                            text: fldname, 
                            flex: 1,
                        xtype: 'gridcolumn'});
                    });            

                    var storeResults = new Ext.data.Store({
                        storeId: 'MyStore1',
                        id: storeId ,
                        proxy: {
                            type: 'jsonp',
                            url : 'http://www.myweb.com/callback.php?loginUsername=' + MyApp.uid + '&loginPassword=' + MyApp.pwd + '&loginIp=' + MyApp.domain + '&level=9&commandid=' + sqlCommandId + '&viewid=' + sqlView + '&params=',
                            reader: {
                                type: 'json',
                                root: 'row'
                            }
                        },
                        fields: modelFields
                    });


                    storeResults.load({
                        scop: this,
                        callback: function(records, operation, success) {
                            if (success) {
                            }
                            console.log(storeResults);
//in the Console If ound that the Store is correctly filled
                            var mygrid = Ext.getCmp('upperdw');
                            console.log(columnNames);
                            mygrid.reconfigure(storeResults, columnNames);
//Here my grid is empty, correct headers without data
                        }});


                    }
                } 
            });

    },

[mitchellsimoens]

Is this question for Ext JS 4?