>>>>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();

>>
>>Hmm. Does 'cnt_code' show up in the list ? If so then it's obviously something strange with 'cnt_pk'
>
>Apparently it is working despite those messages!?

Quite possible - controls will attempt to bind early on and can show this type of error when the DataContext is not set (or not yet populated). Best to just check to trace output when you know there is a problem and look for references to the bindings in question.