I use Cisco AnyConnect Secure Mobility Client on my Windows 8.1 for remote access. It’s been working fine until lately with a message showing me that it failed to initialize connection subsystem.
After a little research, it seems that it’s this Microsoft KB 3023607 update that’s causing Cisco AnyConnect broken. If you go into the KB and you will find the Fix it a the bottom of the page that you can use to fix this problem. Make sure to use Enable this fix it side of button to do the fixing.
Here is another way which may be easier to follow through and work.
1. Close Cisco AnyConnect completely. Make sure no Cisco AnyConnect icon running in the system tray.
2. Open your File Explorer (by pressing Win+E keyboard shortcut), navigate to the following location that holds all Cisco AnyConnect program files.
C:\Program Files (x86)\Cisco\Cisco AnyConnect Secure Mobility Client
3. Right-click vpnui.exe file, and go to Properties.
4. Switch to Compatibility tab, turn on Run this program in compatibility mode for option, and select Windows 8 from the drop-down menu.
5. Click OK, and give it another try.
Note that the compatibility mode has to apply to the executable file directly (vpnui.exe), not the shortcut that points to the executable. That also means, if you have a shortcut pinned on the taskbar, changing the compatibility mode on the pinned shortcut is not going to fix the problem for you. Apply the setting directly to the vpnui.exe file and pin the exe file on to the taskbar.
Hope it helps.