Mac OS X - Cisco VPN Client
If you are running Cisco’s VPN Client on Mac OSX, you might be familiar with (or tormented by) “Error 51: Unable to communicate with the VPN subsystem”. The simple fix is to quit VPN Client, open a Terminal window, (Applications -> Utilities -> Terminal) and type the following from root user: # /System/Library/StartupItems/CiscoVPN/CiscoVPN restart Stopping Cisco Systems VPN Driver kextunload: unload kext /System/Library/Extensions/CiscoVPN.kext succeeded Starting Cisco Systems VPN Driver kextload: /System/Library/Extensions/CiscoVPN.kext loaded successfully