Add vpn connections disabled

[Damian Nadales Agut <D E Nadales Agut tue nl>]

I've seen a lot of posts of users complaining about this. In most of the
cases the problem was that the appropriate plug-ins weren't installed.
But I have installed the pptp, cisco, and openvpn plugins, I've
restarted dbus and the network manager, but the add button is disabled.

I just want to connect to the vpn described here:
    http://www.win.tue.nl/bcf/diensten/netwerk/vpn.php

Thanks in advance,
Damian.