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How to Fix Cisco VPN Client Error 51 – Unable to Communicate with the VPN Subsystem

Apple Mac OS X users are frequently faced with the Cisco VPN Client Error 51 - Unable to Communicate with the VPN Subsystem as shown in the screenshot below:

When this error is produced, users will no longer be able to connect to their VPN using the Cisco VPN client. It seems like Cisco’s VPN client often produces the error when network adaptors disappear and reappear – a common scenario when removing the Ethernet cable or reconnecting to your wireless network.

The solution provided will force the Cisco VPN to re-initialize and continue working without a problem.

To overcome the error, close the VPN Client, open a Terminal Window, (Applications -> Utilities -> Terminal) and type one of the following commands:

For older OS versions:

$ sudo /System/Library/StartupItems/CiscoVPN/CiscoVPN restart

For newer OS versions:

$ sudo kextload /System/Library/Extensions/CiscoVPN.kext

The above command(s) requires administrator rights, so the system might ask for the administrator password as shown below:

Another command that can be used to re-initialize the Cisco VPN subsystem is the following:

$ sudo SystemStarter restart CiscoVPN

Again, the administrator password might be required.

Should the Error 51 problem occur again, simply apply the same command that worked for you previously and you’ll be ready to connect to your VPN. It might also be a good idea to create a small script with the above commends so it can be executed every time the error occurs.

Windows 7/8 users experiencing the Cisco VPN Client Error 442 on their system can also visit our Cisco Services & Technologies section to read how to correct the problem.