If you try to connect to your VPN using Cisco AnyConnect and get the following error after upgrading to Windows 10:
The Client Agent has encountered an error.
The fix is simple, and is the same one as for Windows 8: open regedit and go to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\vpnva. In there, modify the DisplayName key so that it reads Cisco AnyConnect VPN Virtual Miniport Adapter for Windows x64 and restart the VPN client. Once you do that, you should be able to connect to your VPN once more.