THS KK - the PROBMELM WITH SAMPLE PROJECT

Hello Jaroslav!
Sorry for late answer.
I suppose you get the error when you try to use your Show Notes Action.
In this case you have to implement handler for CustomizePopupWindowParams event.
How to do that describes in devexpress documentation in section "Specify the Popup List View".
Please, note that before doing that you should do previous lessons like Set a Many-to-Many Relationship.
Hope this was helpful for you.

Best Regards,
Vitali.