SelectedItem is viewmodel base item. it always show null selectedItem

Tried

            ActiveRecord="{Binding Path=DataContext.SelectedItem, RelativeSource = {RelativeSource FindAncestor, AncestorType={x:Type igDP:XamDataGrid}},
                            Mode=TwoWay, Converter={StaticResource convertNewItemPlaceHolderToNullConverter} }"   

ActiveRecord="{Binding Path=SelectedItem, Mode=TwoWay, Converter={StaticResource convertNewItemPlaceHolderToNullConverter} }"   

thank you.