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I'm working on a mac and recently downloaded the Cisco VPN Client from my company's internal site and when I try to open the application, the icon shows up in my dock and I get an error message saying:

Error 51: Unable to communicate with the VPN Subsystem.
Please make sure that you have at least one network interface that is currently active and has an IP address and start this application again.

Do I need to setup a network interface? Any suggestions are appreciated!

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Did you manage to figure this out? –  Kirk Jun 8 '11 at 2:14
    
yes and no, I'm not able to get the VPN client to launch; however, I'm able to connect to the VPN through my network preferences –  Michael Merchant Jun 9 '11 at 14:45
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3 Answers

up vote 1 down vote accepted

Follow the steps below from this post on Fiberlink's website for an easy to follow/effective method:

  1. Reboot your MAC.
  2. Quit VPNClient, open a Terminal window, (Applications -> Utilities -> Terminal) and type one of the following:

    Older versions:

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

    Newer versions:

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

    You may be prompted for a password, enter it to continue. This will stop and start the "VPN Subsystem".

  3. Repair using Disk Utility
    1. Go into your Application - found in your dock (bottom of your Desktop)
    2. Go to Utilities – found inside the Applications folder
    3. Double-click Disk Utility
    4. Select your HD (hard drive) on the left – mine has the default name of "Macintosh HD"
    5. On the main screen on the right, at the bottom, find the button: "Repair Disk Permissions" and click it
    6. When it is done, you can exit out of this (cmd Q)
  4. Reboot and try to open the Cisco VPN Client again
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thanks for the advice. I ended up giving up on the client and using Apple Network Pref ability to setup a vpn. –  Michael Merchant Jul 13 '11 at 5:32
    
This is good troubleshooting advice. Hopefully, this will help others with this problem –  Michael Merchant Jan 6 '13 at 17:50
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In my case it happened if running the 64-bit kernel (see this Apple support article if you're not sure how to check it).

Here is a Cisco support document that states:

The Cisco IPSec client for Mac OS X does not support the 64 bit kernel. The VPN driver only has i386 and PPC extensions, not x86_64 extensions.

The solution:

hold 3 and 2 simultaneously during startup to boot using the 32-bit kernel (link to Apple support article). The Cisco VPN client should open and function just fine now.

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Have you rebooted since the installation of the VPN client? It sounds like the VPN subsystem is not running properly. I used to have random crashes when I was using the Cisco client on OS X.

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yes, I've tried restarting the system. No luck –  Michael Merchant Jun 8 '11 at 16:57
    
What versions do you have? OS X, VPN Client,etc? Do you use a wired or wireless network? Not using IPv6, right? –  Kirk Jun 8 '11 at 17:03
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