Hi, this one is quite complicated.

I am working on a project with others and we have managed to create a data validation list where the user can choose multiple options.
User clicks "one"
Cell shows one
User clicks "two"
Cell shows one, two
etc...

The problem is, if the user wants to add "fourty" that is not on the data validation list, our code messes up in a weird way and repeats the last selected option several times. (Note that we have turned off the error message that shows for data that is not in the list, in excel.)

Private Sub Worksheet_Change(ByVal Target As Range)
Dim rngDV As Range
Dim oldVal As String
Dim newVal As String
If Target.Count > 1 Then GoTo exitHandler

On Error Resume Next
Set rngDV = Cells.SpecialCells(xlCellTypeAllValidation)
On Error GoTo exitHandler

If rngDV Is Nothing Then GoTo exitHandler

If Intersect(Target, rngDV) Is Nothing Then
   'do nothing
Else
  Application.EnableEvents = False
  newVal = Target.Value
  Application.Undo
  oldVal = Target.Value
  Target.Value = newVal
If Not Intersect(Target, Range("H25:H36")) Is Nothing Then
    If oldVal = "" Then
      'do nothing
      Else
      If newVal = "" Then
      'do nothing
      Else
      Target.Value = oldVal _
        & ", " & newVal
      End If
    End If
  End If
End If

exitHandler:
  Application.EnableEvents = True
End Sub
If you feel you need more information simply ask. I hope one of you can help.