If you’re like me and you use your MacBook Pro for work, it might stand to reason that you have to VPN into your work network. If so, it also may be a good chance that you use the Cisco VPN client and have run into this annoying message:
Error 51: Unable to communicate with the VPN subsystem
Thankfully, the solution is rather simple. Open up your favorite terminal client and simply type:
sudo /System/Library/StartupItems/CiscoVPN/CiscoVPN restart
Enter your password and it’ll restart the subsystem. Then just re-open the Cisco VPN client and you’re golden.