WPF GridView Sort

I have a GridView which binds the customer list. When I click on the headers then it gives me the following error.

I have a method and  I get the error from there. The code is below.

private void Sort(string sortBy, ListSortDirection direction)
        {
                ICollectionView dataView = CollectionViewSource.GetDefaultView(this.ItemsSource);
                dataView.SortDescriptions.Clear();
                SortDescription sd = new SortDescription(sortBy, direction);
                dataView.SortDescriptions.Add(sd);
                dataView.Refresh();
        }

KAdir