How to highlight Access listbox with VBA function that passes listbox name and whether to highlight all or deselect?

Please note code and sample - for some reason its not allowing me to highlight all items when I click a button.  Appreciate any explanation along with the sample fixed.

https://filedb.experts-exchange.com/incoming/ee-stuff/8157-sample_highlight.mdb

Thanks,
Stephen

P.S.  I did try sListBox as ListBox and it didn't work.   I'd rather be shown how to do it both ways - with as a string and a listbox.

Private Sub Highlight_Items(sListBox As String, bShow As Boolean)

  Dim varItem As Variant
  Dim myItem As String
    For Each varItem In Me.Controls(sListBox).ItemsSelected
          'do whatever here in the loop
        
        Me.Controls(sListBox).Selected(varItem) = bShow
        DoEvents
        
    Next varItem
    
    Me.Refresh

End Sub

Private Sub cmdSelAllSource_Click()
  Call Highlight_Items("lstVolume", True)
End Sub

Private Sub cmdUnSelAllSource_Click()
  Call Highlight_Items("lstVolume", False)
End Sub

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