Unchecked all checkbox in a form inside a groupbox inside a panel and another panel

Ok. im getting tired of clearing all checkboxes inside a groupbox inside another panel in my form. i have a code that can clear all checkboxes in my form inside the panel221.

For Each element As Control In Me.Panel221.Controls
        If TypeOf element Is CheckBox Then
            DirectCast(element, CheckBox).Checked = False
        End If
Next

but i dont know why i cant clear all checkboxes in my form by just using this code.

For Each element As Control In Me.Controls
            If TypeOf element Is CheckBox Then
                DirectCast(element, CheckBox).Checked = False
            End If
Next

this is the structured of my form:

-FORM
 -PANEL 1
  -GroupBox 1
   -PANEL 2
     -PANEL 3
       * Several CheckBox inside another panel
     -END OF PANEL 3
   -END OF PANEL 2
  -END OF GROUPBOX 1
   'Another groupbox
  -GroupBox 2
   -PANEL 4
     -PANEL 5
       * Several CheckBox inside another panel
     -END OF PANEL 5
   -END OF PANEL 4
  -END OF GROUPBOX 2
 -END OF PANEL 1
-END OF FORM

so how can i clear or unchecked all that checkbox under a several groupbox and panel? anyone can help me?... thanks a lot! any help will appreciate! sorry for my bad english. Thanks!!!