UltraWinGrid - Disable sorting on few columns

For example, to enable soring only on Column1 and Column4 :

Private Sub UltraGrid1_BeforeSortChange(ByVal sender As Object, ByVal e As
                    Infragistics.Win.UltraWinGrid.BeforeSortChangeEventArgs) Handles
                                                 ugProblemList.BeforeSortChange

       If Not (e.SortedColumns.Exists("Column1") Or 
                    e.SortedColumns.Exists("Column4")) Then
          e.Cancel = True
       End If

End Sub