>Looks like a different problem. What's the ComboBox ItemsSource ?

this is the combo's definition:

<ComboBox Grid.Column="1" Grid.RowSpan="1" Margin="0" Name="cboCountries" VerticalAlignment="Center" 
DisplayMemberPath="cnt_code" SelectedValuePath="cnt_pk" SelectedValue="{Binding cus_cntfk, Mode=Default}" />

and here's the code that sets its itemsource:

this.cboCountries.ItemsSource = this.Country.GetAllEntities();