I do not think it is a reception issue so as to look for repeaters etc.
The router is about 5m (= 15ft) away from the tvbox and has almost visual contact (the router is "hidden" behind a corner). I will make a small sketch to show you if needed, but I do not know how to name various stuff in english.
Also, neither the router, nor the tvbox support 5ghz wireless and the only ethernet cable in the house (the one that connects the router to an old pc) is too short to cover that distance.
Rebooting the router had no effect too. Shall I bite the bullet and delete the forementioned folder?
---edit
I did delete the folder and now le shows all the wireless networks again.
However, it fails to connect to the home's wireless network, poping a notification that something timed out. Any ideas about that?