How to Expand/Collpse ALL Collapsable Panels

Hi,
I have 6 Collpasable panels in my Child page.
Scenorios:
When page loads all Collasible panels should expaded. -> It is working fine.
When I click Collpse All button the above event is firining and all panels are collapsing. This is also working fine. 
When i click again Expand All button this above event is firing but not expanding all panels WHY ?
If user wants to collapse/Expand all  Collapsible Panels at a time on Master Page's Button click How can do that?
Protected Sub btnCollapseExpandAll_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnCollapseAll.Click Dim cpe1 As AjaxControlToolkit.CollapsiblePanelExtender = DirectCast(Me.ContentPlaceHolder1.FindControl("cpe1"), AjaxControlToolkit.CollapsiblePanelExtender) Dim cpe2 As AjaxControlToolkit.CollapsiblePanelExtender = DirectCast(Me.ContentPlaceHolder ...