Windows 10 Preview has just been released and the official advice is to not use it for anything critical just yet, however it is stable and almost everything I've installed so far works as expected. The standard casualties of beta operating systems are VPN clients and this time is not an exception ... well almost.
The Cisco AnyConnect client (version 3.1.05160) installed first time and connected straight away but after a reboot the "failed to initialize connection subsystem" message appeared.
There are two suggestions to fix this, firstly disabling "Work Offline" in Internet Explorer:
Create a new REG DWORD called GlobalUserOffline with a value of 1
In my case this didn't make and difference.
The other suggestion which was successful in my case was to enable Windows 8 compatibility for the launcher:
C:\Program Files (x86)\Cisco\Cisco AnyConnect Secure Mobility Client\vpnui.exe