I have an Excel document with five sheets. On the second sheet there are three codes under Private Sub Worksheet_Change (ByVal Target As Range) that goes like this :

Private Sub Worksheet_Change(ByVal Target As Range)
    If Target.CountLarge > 1 Then Exit Sub 'only handling one-cell changes
    
    DoMessage Target
    HideShowRows Target
    DropDown Target
    
End Sub

The DoMessage Target and HideShowRows are good, they work perfectly. DropDown target doesn’t work. This code is supposed to allow several items in a dropdown list to be chosen by the user simultaneously and non-repetitively. Here’s the code for this one :

Sub DropDown(Target As Range)
Dim Oldvalue As String
Dim Newvalue As String
Application.EnableEvents = True
On Error GoTo Exitsub
If Not Intersect(Target, Range("H11")) Is Nothing Then
    If Target.SpecialCells(xlCellTypeAllValidation) Is Nothing Then
        GoTo Exitsub
    Else: If Target.Value = "" Then GoTo Exitsub Else
        Application.EnableEents = 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 & vbNewLine & Newvalue
            Else:
                Target.Value = Oldvalue
            End If
        End If
    End If
End If
Application.EnableEvents = True
Exitsub:
Application.EnableEvents = True
End Sub

What’s wrong with the code ?