April 27, 2012 - Warren Held

Cisco VPN Client for Mac OS X “Error 51: Unable to communicate with the VPN subsystem”

When you try to run the Cisco VPN Client on a Mac you get “Error 51: Unable to communicate with the VPN subsystem”.  I ran into this issue while trying to get the Mac version of Cisco VPN Client to run on the only Mac user’s system I support.  After a little bit of searching I found out that the user’s system is 64-bit and the Cisco VPN Client only comes in the 32-bit flavor.  The easiest way to get Mac OS X into 32-bit mode is to restart the computer and hold the 3 and 2 keys while it boots.  Likewise, if your Mac normally boots in 32-bit mode you can hold down the 6 and 4 keys to get it to boot into 64-bit mode.  You can check to see what architecture you are running by running this command in the terminal:

[bash]systemsetup -getkernelbootarchitecturesetting[/bash]

To set your machine to always boot into 32 bit mode enter this command and reboot:

[bash]sudo systemsetup -setkernelbootarchitecture i386[/bash]

To set your machine to always boot into 64 bit mode enter this command and reboot:

[bash]sudo systemsetup -setkernelbootarchitecture x86_64[/bash]

Cisco Cisco / OS X /