I want to show mask from codebehind ! but mycode doesn't work

Code:

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Protected Sub buton(ByVal sender As Object, ByVal e As AjaxEventArgs)
    Dim mymask As New Coolite.Ext.Web.Mask.Config
    mymask.Msg = "please wait"
    Ext.Mask.Show(mymask)
    Dim i As Integer
    For i = 0 To 100000000
    Next
    Ext.Mask.Hide()
End Sub

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