Install Cisco VPN Client on MacOS X 10.5
Installing an older version of the Cisco VPN Client on Mac OS X 10.5 (Leopard) will not work out. When trying to open the VPN Client Application, you'll only get the following error message: "Error 51: Unable to communicate with the VPN subsystem."
Solution
You need at least version 4.9.01.0100, which introduces Support for Mac OS X 10.5.
Details can be found in NachtJogger's Blog post.
