Auto Upper Case Problems

I am using the code below to force everything to upper case

Private Sub Worksheet_Change(ByVal Target As Range)
    If Not (Application.Intersect(Target, Range("A1:B10")) _
      Is Nothing) Then
        With Target
            If Not .HasFormula Then
                Application.EnableEvents = False
                .Value = UCase(.Value)
                Application.EnableEvents = True
            End If
        End With
    End If
End Sub

Works fine until i wast to copy a cell by dragging down, then i get this

Run Time Error 13
Type Mismatch

Is there a way to force upper case and allow me to copy from say a1 to a2:a20

Thanks

Graham