So i installed Windows 8 release preview on my desktop a few days ago and so far i've been quite impressed with it.
One problem that i've come across so far is that after upgrading, Cisco vpn client stopped working with a "Failed to enable Virtual Adapter" error when i tried to connect to any vpn.
This is massively annoying for me as i use Cisco vpn client to connect to the network at work.
Fortunately after some frantic googling i managed to find a workaround.
Fire up the registry editor and navigate to the following path.
Modify the DisplayName key
For 64bit Windows, edit the key so that it reads "Cisco Systems VPN Adapter for 64-bit Windows", or for x86 "Cisco Systems VPN Adapter"
Now open the vpn client and try connecting again. It should work now.
Hopefully this post will save someone else a bit of time.