telerik test studio - RadComboBox Cell text in RadGridGriew -

am recording web application. silver light application.i have radgridview column radcombobox:

when selecting item radcombobox item not selecting while running.that step failing.

find below code :

silverlightapp app = activebrowser.silverlightapps()[0]; radgridview grid = app.find.byautomationid<radgridview>("radgridviewname"); assert.isnotnull(grid); gridviewrow row = grid.rows[2]; row.user.click(mouseclicktype.leftdoubleclick);  telerik.webaii.controls.xaml.radcombobox    cb=row.find.bytype<telerik.webaii.controls.xaml.radcombobox>();  cb.selectitem("football", true); system.threading.thread.sleep(1000); 

but getting out of index error. let me know doing mistake....