This is a weird one. When you go to:
1. Browse Cameras on the top menu bar and type in AGFA
2. The results work fine but when you go to page 4 or beyond you get a 404 page.
You can change that of course, but as the warning message says, the posts per page count must also be changed under the Settings -> Reading panel in WordPress Core settings (because it can’t be changed from the plugin back-end unfortunately).