VPN with network manager (nm-applet) is not working

nm-applet only talks to network-manager (over d-bus); messages of network-manager itself are sent to syslog, tail -f /var/log/syslog will show you what is going on while it is trying to connect:

Aug  4 12:01:59 flux NetworkManager[1085]: <info> Starting VPN service 'vpnc'...
Aug  4 12:01:59 flux NetworkManager[1085]: <info> VPN service 'vpnc' started (org.freedesktop.NetworkManager.vpnc), PID 10062
Aug  4 12:02:00 flux NetworkManager[1085]: <info> VPN service 'vpnc' appeared; activating connections
Aug  4 12:02:00 flux NetworkManager[1085]: <info> VPN plugin state changed: 3
Aug  4 12:02:00 flux NetworkManager[1085]: <info> VPN connection 'Something' (Connect) reply received.
Aug  4 12:02:00 flux NetworkManager[1085]:    SCPlugin-Ifupdown: devices added (path: /sys/devices/virtual/net/tun0, iface: tun0)
Aug  4 12:02:00 flux NetworkManager[1085]:    SCPlugin-Ifupdown: device added (path: /sys/devices/virtual/net/tun0, iface: tun0): no ifupdown configuration found.
Aug  4 12:02:00 flux NetworkManager[1085]: <info> VPN connection 'Something' (IP Config Get) reply received.
Aug  4 12:02:00 flux NetworkManager[1085]: <info> VPN Gateway: *******
Aug  4 12:02:00 flux NetworkManager[1085]: <info> Tunnel Device: tun0
Aug  4 12:02:00 flux NetworkManager[1085]: <info> Internal IP4 Address: 10.16.7.37
Aug  4 12:02:00 flux NetworkManager[1085]: <info> Internal IP4 Prefix: 20
...
Aug  4 12:02:01 flux NetworkManager[1085]: <info> Clearing nscd hosts cache.
Aug  4 12:02:01 flux NetworkManager[1085]: <info> VPN connection 'Something' (IP Config Get) complete.
Aug  4 12:02:01 flux NetworkManager[1085]: <info> Policy set 'Auto eth0' (eth0) as default for IPv4 routing and DNS.
Aug  4 12:02:01 flux NetworkManager[1085]: <info> VPN plugin state changed: 4

and so on. It is not always terribly informative (especially if VPNC authentication fails), but nevertheless useful.