Windows L2TP VPN / Dial Up Networking
Users get this error when they attempt to connect to a VPN server and there is a problem with the encryption.
If this is a new VPN setup, check your settings in your VPN client vs what information you were given from your VPN
server admin. One of the simplest errors is that users leave the settings on the default "Use L2TP/IPSec" for
encryption and click ok, instead of picking the second check box which is the Microsoft "PPTP". If you are VPNing into
a Cisco, or Lucent or Nokia server, it will most likely be IPSec. If
you are VPNing into your small office Windows
Server, it will most likely be 'PPTP'.
If you do require a certificate to connect to your VPN server, you will want to talk to your VPN server admins. They
usually push a certificate to your PC (from SMS/SCCM) and it's automatically saved/installed on your PC/laptop. If
that's not the case, there might need to be some form of manual install of the certificate on your PC/laptop.
If it worked, and there have been no changes to your PC, talk to your helpdesk, there might be a server issue and the
server admins might need to stop and restart a process or two (or the server itself..).
Link to Microsoft Support Article