I will give the solution here to 2 annoying problems that I have encountered in Ubuntu 16.04 with VPN settings.
The VPN connection to ... has failed because of invalid VPN secrets.
Network manager has no option to add openVPN, only point to point tunneling protocol connections.
These two issues are related, or I strongly assume, and the solution is to install some packages,
sudo apt-get install network-manager-openvpn network-manager-openvpn-gnome network-manager-pptp network-manager-vpnc
|After installing the above packages, OpenVPN is back in the network manager.|
To aply changes you may have to restart the network manager with
sudo service network-manager restart
or simply reboot your computer.