If you upgrade to Mac OS 10.6 Snow Leopard you might need to reinstall the BOL Cisco vpn client: https://www.bol.ucla.edu/pub/bol/vpn/software/vpnmac-4.9.01.0180.dmg.zip

Alternately, users can uninstall the Cisco client (via the command-line, using “sudo /usr/local/bin/vpn_uninstall” in Terminal), and use the Snow Leopard built-in VPN client, which can be accessed from System Preferences→Network, and also features a convenient VPN control in the menu bar.