Windows 10: Getting an error when connecting to VPN "The L2TP connection attempt failed .."

Hi, I am having an error when conencting to VPN, "The L2TP connection attempt failed because the security layer encountered a processing error during initial negotiations with the remote computer." It's weird because I was just able to connect last week, all of a sudden it is having this error.I just installed Windows 11 hoping that it would be solved but did not at all I had Windows 10. Last update was 07/14/2023, but I was able to connect to the VPN between 07/15/23-07/27/23, then the latest update would be today 08/01/2023, so unsure if this is an update issue? Any help would be apprecia

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VPN - "The L2TP connection attempt failed because security policy for the connection was not found".

Connecting Windows 10 VPN to Draytek routers on numerous sites all returns the same error. Sometimes a reboot works, sometimes it doesn't. Have followed all steps in the similar message (The L2TP connection attempt failed because the security layer encountered a processing error during the initial negotiations with the remote computer), but this error of mine is "security policy not found". Where is the security policy and why does it have a problem finding it sometimes??

 

Error: 788, when connecting to L2TP VPN

Hi there, recently I got this error when connecting to "L2TP/IPSec with certificate" VPN. I'm not sure what cause this.

I have already follow some of this steps with no luck :

• Adding AssumeUDPEncapsulationContextOnSendRule
• Restarting both IKE and IPSec services
• Allowing both CHAP and MS-CHAP v2
• Reset network connection
• Connect to different provider
• Re-adding VPN settings

There also little bit information can be found in the event viewer :

CoId={AEE0E2A8-34DF-41BB-B5F0-0458EFD41751}: The user xxx\xxx has started dialing a VPN connection using a per-user connection profile named yes. The connection settings are:

Dial-in User = *\

VpnStrategy = L2TP

DataEncryption = Requested

PrerequisiteEntry =

AutoLogon = No

UseRasCredentials = Yes

Authentication Type = PAP

Ipv4DefaultGateway = Yes

Ipv4AddressAssignment = By Server

Ipv4DNSServerAssignment = By Server

Ipv6DefaultGateway = Yes

Ipv6AddressAssignment = By Server

Ipv6DNSServerAssignment = By Server

IpDnsFlags =

IpNBTEnabled = Yes

UseFlags = Private Connection

ConnectOnWinlogon = No

IPsec authentication for L2TP = Machine certificate.

CoId={AEE0E2A8-34DF-41BB-B5F0-0458EFD41751}: The user xxx\xxx is trying to establish a link to the Remote Access Server for the connection named yes using the following device:

Server address/Phone Number = xxx.xxx.xxx.xxx

Device = WAN Miniport (L2TP)

Port = VPN3-1

MediaType = VPN.

CoId={AEE0E2A8-34DF-41BB-B5F0-0458EFD41751}: The user xxx\xxx dialed a connection named yes which has failed. The error code returned on failure is 788.

***Original title: VPN Error 788***

 

L2TP Connection attempt failed - April 2022 (SOLVED)

I set up a clients computer before Christmas and configured a L2TP with preshared key VPN which had been working without issues up until a few weeks ago. I can confirm that the following is in place:

• All ports corrected forwarded.
  
• Regedit - AssumeUDPEncapsulationContextOnSendRule / DWORD (32 bit) Value = 2
  
• Adapter PPP settings - Enable LCP extensions (ticked for use)
  
• Adapter Security tab - Allow these protocols / Challenge Handshake Authentication Protocol (CHAP) & Microsoft CHAP Version 2 (MS-SHAP v2)
  
• All Windows updates applied
  

I understand that L2TP was broken around January, and then a patch released, with this computer up to date with updates. As a test, I configured my own computer (which had a fresh Windows 11 install a month ago) and is fully up to date with updates, and get the same errors when trying to connect.

So I am at a loss as to why this is 'still' broken even though both computers are now up to date. I'm still getting the following error:

The L2TP connection attempt failed because the security layer encountered a processing error during the initial negotiations with the remote computer.

Any suggestions would be much appreciated. I'm connecting to a Synology NAS. Searches for this error return the update issue from earlier this year, and have not found any further recent information.