>It answers my question (ie DataContext is mmBindingList) but doesn't help me answer yours since I know BA about MM :-{
>

At first I couldn't figure out what the B in BA stood for, but I then realised you are in the UK. :)

>I'm assuming the grid is not the standard WPF Datagrid either so this may be something a MM guy can answer better although it looks OK to me. Have you checked the Output window to see if that shows any binding errors. It might be worth configuring the app to list binding errors during development; see :http://stackoverflow.com/questions/337023/how-to-detect-broken-wpf-data-binding for info on how to set up app.config for this....

The output window showed me some binding errors due to incorrect case in the bindings. I changed those but still had the problem, so I added in the suggested configuration to my app.config and this is some of the text generated in the text file:

System.Windows.Data Information: 40 : BindingExpression path error: 'cnt_pk' property not found for 'object' because data item is null. This could happen because the data provider has not produced any data yet. BindingExpression:Path=cnt_pk; DataItem=null; target element is 'ComboBox' (Name='cboCountries'); target property is 'NoTarget' (type 'Object')
System.Windows.Data Information: 19 : BindingExpression cannot retrieve value due to missing information. BindingExpression:Path=cnt_pk; DataItem=null; target element is 'ComboBox' (Name='cboCountries'); target property is 'NoTarget' (type 'Object')
System.Windows.Data Information: 20 : BindingExpression cannot retrieve value from null data item. This could happen when binding is detached or when binding to a Nullable type that has no value. BindingExpression:Path=cnt_pk; DataItem=null; target element is 'ComboBox' (Name='cboCountries'); target property is 'NoTarget' (type 'Object')
System.Windows.Data Information: 10 : Cannot retrieve value using the binding and no valid fallback value exists; using default instead. BindingExpression:Path=cnt_pk; DataItem=null; target element is 'ComboBox' (Name='cboCountries'); target property is 'NoTarget' (type 'Object')

Does that look like it could be a problem?