I have two RasPi3, both on the newest Jessie and updated && upgraded. The problem is that both Pis can see networks but are not connecting to them.
sudo iwlist wlan0 scan
Gives me multiple networks including the one I want to connect to. Typing in the credentials and authentication into the wpa_supplicant.conf file doesn't work. Then I installed xrdp on the Pis to see if a connection over that is possible. Again I see available networks including the one I want to connect to. I click it, type in the requested key and nothing happens. Afterwards a mouseover on the networks button in the upper right corner shows "wlan0 not associated".
sudo ifup wlan0
tells me that the wlan0 interface is already configured. Makes sense. The newest firmware for the WiFi chip on the board is installed.
When I set the Pis up, they connected without any problems. Even to the same network as they should now. Nothing changed in the meantime.
What can I try?
EDIT: Just tested to connect to my phone using the mobile hotspot. No problem at all...It gets confusing.