Problem updating a cell value

Hi all,

I have code which I am trying to use to update a cell with a revised 'date of birth'. The VBA fires on AfterUpdate event of a field called DOB on a userform.

Private Sub DOB_AfterUpdate()

                Dim Res As Long
                Res = Application.Match(CTOID, Sheets("TreatmentOrders").Range("A:A"), 0)
                MsgBox "Res = " & Res
                If Not IsError(Res) Then
                        Sheets("TreatmentOrders").Range("D" & Res).Value = Me.DOB.Value
                        MsgBox "Updated DOB"
                End If

        'Me.DOB = Format(Me.DOB, "d mmmm yyyy")
        'Me.NewCTODate.SetFocus
        
End Sub

Problem is, I am getting error 13 Type Mismatch on the second line.

Any clues anyone?

cheers
Pete