Unable to get Show detail Property of the Pivot Item Class

Error 1004 as "Unable to get Show detail Property of the Pivot Item Class

when I tried to execute below code to expand the pivot table rows. Please provide the solution

Private Sub CommandButton1_Click()

'Expand the lowest position field in the Rows area
'that is currently expanded (showing details)

Dim pt As PivotTable
Dim pf As PivotField
Dim pi As PivotItem
Dim iFieldCount As Long
Dim iPosition As Long

  'Create reference to 1st pivot table on sheet
  'Can be changed to reference a specific sheet or pivot table.
  Set pt = ActiveSheet.PivotTables(1)

  'Count fields in Rows area minus 1 (last field can't be expanded)
  iFieldCount = pt.RowFields.Count - 1

  MsgBox iFieldCount

  'Loop by position of field
  For iPosition = 1 To iFieldCount

      MsgBox iPosition
    'Loop fields in Rows area
    For Each pf In pt.RowFields
      'If position matches first loop variable then
      If pf.Position = iPosition Then
        'Loop each pivot item
        For Each pi In pf.PivotItems
          'If pivot item is collapsed then
            If pi.ShowDetail = False Then
            'Expand entire field
            pf.ShowDetail = True
            'Exit the macro
            Exit Sub
          End If
        Next pi
      End If
    Next pf
  'If the Exit Sub line is not hit then the
  'loop will continue to the next field position
  Next iPosition

End Sub