Comment 1 for bug 1651458

I confirm this problem. It seems to have appeared at sone tine after (but not immediately with) release of OTA-14.
Although VPN configuration has not changed, I cannot establish VPN connections via system indicator or system settings. Sliding the switch immediately displays the massage: Connection failed, because there was no valid configuration data.
I have tried re-entering the password in VPN settings, even deleting connection data and re-creating it via system settings, to no avail.
As Frindli correctly describes, the VPN connection can be established from the terminal, using
sudo nmcli con up VPNNAME
But this asks for the VPN password. So it appears that the password is not stored any longer when creating the VPN configuration using system settings.
As said before, this used to work until late 2016.