VBA Code Not Working On Saved Book

[RebuildToday3]

My VBA code used to work and I cannot get it to work again. It is only on the saved file. If I open a blank new excel sheet and insert the code it works there. I'm not sure what to do to fix it as I've tried all I know. I'm wanting to have a column of drop-down menus. These menus have multiple selections without repetition is my plan. It used to work on my saved book and doesn't now. It will only select one from the drop-down menu, not multiple, yet works on a new book.

CODE I HAVE:

Private Sub Worksheet_Change(ByVal Target As Range)
' To allow multiple selections in a Drop Down List in Excel (without repetition)
Dim Oldvalue As String
Dim Newvalue As String
Application.EnableEvents = True
On Error GoTo Exitsub
If Target.Column = 5 Then
  If Target.SpecialCells(xlCellTypeAllValidation) Is Nothing Then
    GoTo Exitsub
  Else: If Target.Value = "" Then GoTo Exitsub Else
    Application.EnableEvents = False
    Newvalue = Target.Value
    Application.Undo
    Oldvalue = Target.Value
      If Oldvalue = "" Then
        Target.Value = Newvalue
      Else
        If InStr(1, Oldvalue, Newvalue) = 0 Then
            Target.Value = Oldvalue & ", " & Newvalue
      Else:
        Target.Value = Oldvalue
      End If
    End If
  End If
End If
Application.EnableEvents = True
Exitsub:
Application.EnableEvents = True
End Sub

 

[Fluff]

Is the sheet protected?

 

[JLGWhiz]

Try running this code from module1.

Sub reset()
Application.EnableEvents = True
End Sub

Then try the event code.

 

[mikerickson]

Was the book saved as Macro Enabled?