Datagrid problem

can somebody help me?
let me explain more
My datagrid’s data is populated from parsing xml in it by xml con and dataset
In the Xml file i have afield ( student name)
And in flash i create a checkbox in taketime column of the datagrid, the dataset inspector schema has student name and taketime

and in the movieclip

import mx.controls.DataGrid;
// Build data provider for the data grid 
myDP = new Array();
student_dg.dataProvider = myDP;  
student_dg.getColumnAt(1).cellRenderer = "CheckBoxCell";

The cellrender code:

import mx.core.UIComponent;
import mx.controls.CheckBox;
class CheckBoxCell extends UIComponent {
 private var check:MovieClip;
 private var listOwner:MovieClip;
 private var getCellIndex:Function;
 function CheckBoxCell() {
 private function createChildren():Void {
  check = createObject("CheckBox", "check", 1, {styleName:this, owner:this});
  check.addEventListener("click", this);
 private function size():Void {
  check.setSize(__width, __height);
  check._x = 0;
  check._y = 0;
 private function setValue(str:String, item:Object, sel:Boolean):Void {
  check._visible = (item != undefined);
  check.selected = item.selected;
  check.label = item.label;
 private function getPreferredHeight():Number {
  return 16;
 private function click() {
  listOwner.dataProvider.editField(getCellIndex().itemIndex, "selected", check.selected);
  listOwner.dataProvider.editField(getCellIndex().itemIndex, "label", **_root.clock.time**);

the bold text is what my problem, the i want to check the checkbox and that checkbox label will show the current time,
but now , the label of the checkbox displays undefined and the checkbox isnt allowing me to tick it