Listpicker error SelectedItem must always be set to a valid value

Question

I have a page in a Windows Phone 7 app where the user can edit or delete an Transaction object. The Transaction object is an Linq-to-Sql class that have a relationship with

Answer 1

This error may also be caused by the order of the XAML properties:

This does NOT work (throws the exception because the ItemsSource is null when the SelectedItem is set):

This works as the itemssource is initialized first: