TreeView, ошибка уникального ключа / object variable - VB

Option Explicit
____________________

Private Sub Worksheet_SelectionChange(ByVal Target As Range)

Dim LastRow As Integer
Dim LastCol As Integer
Dim LastCell As Integer

Dim Key_, modul_, modul As String
Dim i As Integer
Dim nodX As Node

TreeView22.Nodes.Clear

modul = Worksheets("Лист2").Cells(1, 1).Value
nodX = Me.TreeView22.Nodes.Add(, , "a1", modul)

Key_ = "a1"
Worksheets("Лист1").Select
For i = 1 To 11
 modul_ = Worksheets("Лист2").Cells(i, 1).Value
 If modul <> modul_ Then
   Set nodX = TreeView22.Nodes.Add(, , "a" & i, modul_)
   Key_ = "a" & i
   modul = modul_
   Set nodX = TreeView22.Nodes.Add(Key_, tvwChild, "b" & i, Worksheets("Лист2").Cells(i, 2).Value)
 Else
   Set nodX = TreeView22.Nodes.Add(Key_, tvwChild, "b" & i, Worksheets("Лист2").Cells(i, 2).Value)
 End If
Next i

End Sub

nodX = Me.TreeView22.Nodes.Add(, , "a1", modul)