Well, after updating my system to Windows 8.1, I have discovered that the update seems to have broken my AT&T VPN client. This is what I use to access the network where I work. Everything else about the upgrade went smooth.
After some quick searches, I found that people are reporting that many other VPN clients have been affected by Windows 8.1 as well. There are many different attempts to get things working again. Most people are having the best luck with uninstalling the VPN software and then doing a completely fresh install while running the installer as the Administrator.
Just for kicks, I went to Control Panel and tried to do a repair of the AT&T VPN client. After the repair, I rebooted for good measure. When I logged in, I found that the repair hadn’t helped a thing, so I started the client uninstall process. After another reboot and a nice fresh re-install, the AT&T VPN client is working once again.
Your mileage may vary with this solution depending on what VPN client you are using, so good luck.