Sisco VPN ERROR 51
繰り返しメッセージが出たら、VPNの再起動が必要。
$ sudo /System/Library/StartupItems?/CiscoVPN/CiscoVPN restart
詳しくは
http://www.anders.com/cms/192/CiscoVPN/Error.51:.Unable.to.communicate.with.the.VPN.subsystem
http://www.cisco.com/japanese/warp/public/3/jp/service/manual_j/sec/vpncl/ugm/chapter02/install.html