wpf - How to clear and add SortDescriptor to a Telerik DataGrid?

Question

I am developing a WPF application that uses Telerik controls (http://www.telerik.com/help/silverlight/gridview-sorting-programmatic.html). I want to clear the sorting descriptor and then I want to add it again.

I clear the sortingDescriptors:

 grdPatients.SortDescriptors.Clear();

then I add the sortingdescriptor with the following code:

       grdPatients.SortDescriptors.Add(new Telerik.Windows.Data.SortDescriptor()
        {
          Member = "Patient.Name",
          SortDirection = System.ComponentModel.ListSortDirection.Ascending
        });

but the sorting is not applied.

Am I missing something?

SOLVED: The problem was at the Sort Descriptor Member :"Patient.Name"