Cisco IPSec Issue with Windows 10

Though I'm not sure that the VPN type was identical, when I got the error message The L2TP connection attempt failed because the security layer encountered a processing error during initial negotiations with the remote computer, the only thing I had to do is described by the third option on this blog. I copy it here in case the link goes bad:

• IKE and AuthIP IPsec Keying Modules disabled: Solution: This occurs most often when 3rd party VPN software has been installed and disables the IKEEXT service. This can be re-enabled by navigating in Windows to Control Panel > Administrative Tools > Services. Find the service named “IKE and AuthIP IPsec Keying Modules” and open it. Change the Startup type to “Automatic”. it may be necessary to remove the 3rd party VPN software.

In my case, I didn't have to uninstall any 3rd party VPN software. I happened to be running Windows 10 (1803) at the time.