I have XnView 1.96.2 and QuickView Plus 9.0.0. When I associate files with XnView, it looks okay, but associated files opens in QuickView Plus, and not XnView. After uninstalling QuickView Plus, everything works as it should. 
I do not know if the culprit is QuickView Plus, XnView or both. Is this a known problem, and what could  the reason be?
Regards,
Hans L