Today, last update of Policykit, Network-Manager-Applet started to missbehave, saying  you are not allowed to change or join a network the solution is this :

you need to create a file

filename:

org.freedesktop.NetworkManager.pkla 

with this inside

[nm-applet]
Identity=unix-group:netdev
Action=org.freedesktop.NetworkManager.*
ResultAny=yes
ResultInactive=no
ResultActive=yes

in this folder

/etc/polkit-1/localauthority/50-local.d

The same error started to show up with removable drives, I will look  for a solution then.