When using the Cisco VPN Client from off-campus, sometimes it will throw an error on launch and prevent you from connecting to the VPN concentrator. (The specific error is "Error 51: Unable to communicate with the VPN subsystem.")
Usually, you can fix this by opening up Terminal and entering the following command at the command prompt (followed by hitting "Enter"):
sudo /System/Library/StartupItems/CiscoVPN/CiscoVPN restart
However, if you run into Error 51 on the first launch of VPNClient, you'll get the following error:
sudo: /System/Library/StartupItems/CiscoVPN/CiscoVPN: command not found
In this case, deleting VPNClient from /Applications and reinstalling the latest version should fix the problem. (A reboot also might do the trick.)
Another error that you may encounter is "Error 5: No hostname exists for this connection entry. Unable to make VPN connection." In this case, right-click the Stanford_Public_VPN connection entry in the connection window and choose Modify from the contextual menu. In the host field, enter su-vpn.stanford.edu and click Save. (Uninstalling and reinstalling also should fix this problem.)
