I create a window like this

Code:
_target = new Ext.Window({                layer: 'top',
                width: _width,
                height: _height,
                constrainTo: aBody,
                constrain: true,
                renderTo: aBody,
                autoScroll: true,
                flex: 1,
                modal: (targetParams.Modal != undefined) ? targetParams.Modal : false,
                resizable: (targetParams.Resizable != undefined) ? targetParams.Resizable : true,
                minimizable: (targetParams.Minimizable != undefined) ? targetParams.Minimizable : true,
                maximizable: (targetParams.Maximizable != undefined) ? targetParams.Maximizable : true,
                closable: (targetParams.Closable != undefined) ? targetParams.Closable : true,
                maximized: _maximized,
                minimzed: _minimized,
                isInFront: true
            });
I noticed that the objects created in each version are quite different. I then do this:

Code:
_target.on("render", function (items) {                    if (items.length > 0) {
                        this.show();
                        this.add(items);
                        this.doLayout();
                        var buttonText = targetParams.ButtonText || this.title;
                        createToolbarButton(this.id, buttonText, targetParams.UIConfigurationId);
                    }
                    else {
                        _target.destroy();
                    }
                });
The problem is on the highlighted line. On 4.0 this line calls this function

Code:
show : function() {        this.callParent(arguments);
        this.performDeferredLayouts();
        return this;
    },
But on the 4.1 the same line calls another function:

Code:
show: function(animateTarget, cb, scope) {        var me = this;


        if (me.rendered && me.isVisible()) {
            if (me.toFrontOnShow && me.floating) {
                me.toFront();
            }
        } else if (me.fireEvent('beforeshow', me) !== false) {
            me.hidden = false;


            
            if (!me.rendered && (me.autoRender || me.floating)) {
                me.doAutoRender();
            }
            if (me.rendered) {
                me.beforeShow();
                me.onShow.apply(me, arguments);


                
                
                if (me.ownerCt && !me.floating && !(me.ownerCt.suspendLayout || me.ownerCt.layout.layoutBusy)) {
                    me.ownerCt.doLayout();
                }
                me.afterShow.apply(me, arguments);
            }
        }
        return me;
    },
In which down the line tries to do
Code:
layout.renderChildren()
and then it gives an error.

I think it's obvious that the objects created are different, but i haven't seen this question addressed in the "Upgrade 4.0 to 4.1" document.

So my question is what i have to do to make this work?

Thanks in advance for the help.