我在 Fritzbox 上配置了 VPN 访问。现在我尝试在 CentOS 6 机器上设置 VPN 客户端。为此，我安装了 vpnc 和 NetworkManager-vpnc，并按照以下说明操作http://tosit.de/aktuelles/vpn-verbindung-unter-ubuntu-zu-fritzbox.html
但每次我尝试连接 VPN（从命令行“vpnc”）时，都会收到错误
vpnc: vpnc.c:1166: lifetime_ike_process: Assertion `0' failed.
此外，如果我尝试使用启用了调试输出（nm-vpnc-service --debug）的 networkManager，我会得到：
** Message: <info> vpnc started with pid 13161
vpnc: vpnc.c:1166: lifetime_ike_process: Assertion `0' failed.
** (process:13150): WARNING **: <WARN> vpnc_watch_cb(): vpnc died with signal 6
在 /var/log/message （客户端）中我得到：
Dec 18 19:02:30 lifebook01 NetworkManager[12964]: <info> Starting VPN service 'org.freedesktop.NetworkManager.vpnc'...
Dec 18 19:02:30 lifebook01 NetworkManager[12964]: <info> VPN service 'org.freedesktop.NetworkManager.vpnc' started (org.freedesktop.NetworkManager.vpnc), PID 13282
Dec 18 19:02:30 lifebook01 NetworkManager[12964]: <info> VPN service 'org.freedesktop.NetworkManager.vpnc' appeared, activating connections
Dec 18 19:02:30 lifebook01 NetworkManager[12964]: <info> VPN plugin state changed: 1
Dec 18 19:02:35 lifebook01 NetworkManager[12964]: <info> VPN plugin state changed: 3
Dec 18 19:02:35 lifebook01 NetworkManager[12964]: <info> VPN connection 'Fritzbox test' (Connect) reply received.
Dec 18 19:02:35 lifebook01 kernel: tun0: Disabled Privacy Extensions
Dec 18 19:02:35 lifebook01 NetworkManager[12964]: <info> VPN plugin state changed: 6
Dec 18 19:02:35 lifebook01 NetworkManager[12964]: <info> VPN plugin state change reason: 0
Dec 18 19:02:35 lifebook01 NetworkManager[12964]: <warn> error disconnecting VPN: Could not process the request because no VPN connection was active.
Dec 18 19:02:35 lifebook01 NetworkManager[12964]: <info> Policy set 'System eth0' (eth0) as default for IPv4 routing and DNS.
有人知道这里的问题是什么或者我如何才能获得更好的错误消息？