Hello, I have some code about TreeGrid

<script type="text/javascript">
       function nodeLoad(node) {
            Ext.net.DirectMethods.NodeLoad(node.id, {
                success: function (result) {
                    var data = eval("(" + result + ")");
                    node.loadNodes(data);
                },
                failure: function (errorMsg) {
                    Ext.Msg.alert('Failure', errorMsg);
                }
            });
        }

        var RemoveItemOnGrid = function () {
            Ext.Msg.confirm('Confirm', 'Do you want to delete ?', function (btn) {
                if (btn == "yes") {
                    if (hdfRecordID.getValue() == "") {
                        alert('You do not select record');
                        return false;
                    }
                    try {
                        grid.getRowEditor().stopEditing();
                    }
                    catch (e) {

                    }
                    var id = hdfRecordID.getValue().toString();
                    Ext.net.DirectMethods.DeleteNode(id);
                    TreeGrid1.getRootNode().reload();
                    return true;
                }
            });
        }
</script>
                <ext:Hidden runat="server" ID="hdfRecordID" />
                <ext:TreeGrid ID="TreeGrid1" runat="server" StripeRows="true" TrackMouseOver="true"
                     AnchorHorizontal="100%" NoLeafIcon="true" AutoExpandColumn="NAME" EnableDD="true" Border="false">
                            <TopBar>
                                <ext:Toolbar runat="server" ID="Toolbar1">
                                    <Items>
                                        <ext:Button ID="btnAdd" runat="server" Text="Addi" Icon="Add">
                                            <Listeners>
                                                <Click Handler="#{wdAddWindow}.show();" />
                                            </Listeners>
                                        </ext:Button>
                                        <ext:Button ID="btnEdit" runat="server" Disabled="true" Text="Edit" Icon="Pencil">
                                            <Listeners>
                                                <Click Handler="#{wdAddWindow}.show();" />
                                            </Listeners>
                                            <DirectEvents>
                                                <Click OnEvent="btnEdit_Click" />
                                            </DirectEvents>
                                        </ext:Button>
                                        <ext:Button ID="btnDelete" runat="server" Text="Delete" Disabled="true" Icon="Delete">
                                            <Listeners>
                                                <Click Handler="RemoveItemOnGrid();" />
                                            </Listeners>
                                        </ext:Button>
                                        <ext:ToolbarSeparator ID="ToolbarSeparator1" runat="server" />
                                    </Items>
                                </ext:Toolbar>
                            </TopBar>
                            <Columns>
                                <ext:TreeGridColumn Header="PR_KEY" Width="150" DataIndex="PR_KEY" />
                                <ext:TreeGridColumn Header="NAME" Width="150" DataIndex="NAME" />
                                <ext:TreeGridColumn Header="NOTES" Width="150" DataIndex="NOTES" />
                            </Columns>
                            <Root>
                                <ext:AsyncTreeNode NodeID="0" Text="Root" />
                            </Root>
                            <SelectionModel>
                                <ext:DefaultSelectionModel runat="server" ID="DefaultSelectionModel1">
                                    <Listeners>
                                        <SelectionChange Handler="#{hdfRecordID}.setValue(node.id); " />
                                    </Listeners>
                                </ext:DefaultSelectionModel>
                            </SelectionModel>
                            <Listeners>
                                <BeforeLoad Fn="nodeLoad" />
                                <DblClick Handler="#{wdAddWindow}.show();" />
                            </Listeners>
                            <DirectEvents>
                                <DblClick OnEvent="btnEdit_Click">
                                    <EventMask ShowMask="true" Msg="Please wait..." />
                                </DblClick>
                            </DirectEvents>
                        </ext:TreeGrid>
When I select a record and click Delete button, I use
TreeGrid1.getRootNode().reload();
to refresh tree.
But my tree not refresh and firefox show error "TypeError: node is null"