You can get below VPN Client Error at user side sometime.
Reason 412:The remote peer is no longer responding.
You would see a lot of resolving method on Internet for user side.
But the above error is not from User side. It is come out from your Network (Firewall, IPS, Server) actually.
The error mentioned that client couldn't get DHCP, Default Gateway and DNS setting from your Network when they are requesting.
For example, Dynamic Host Configuration Protocol Filter has been blocked from IPS in my network actually.
After I permit this filter, all my VPN Client able to connect VPN Connection successfully.
So, you should look at your IPS or Firewall that could filter DHCP Request if you also facing this kind of issue.
Have a good time.
(Be knowledgeable, pass it on then)