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The error message: “The L2TP connection attempt failed because the security layer encountered a processing error during initial negotiations with the remote computer” is commonly referred to as VPN error 789. This is one of the most common VPN errors that occurs when a user tries to connect to L2TP. Here, the L2TP connection attempt failed because the security layer encountered a processing error during the first negotiation with the remote computer.
The error message: “The L2TP connection attempt failed because the security layer encountered a processing error during the first negotiation with the remote computer” is a common error to determine when the IPSec negotiation fails for L2TP/IPSec connections. It is only caused by a misconfiguration of the user’s operating system.
Possible causes of “The L2TP connection attempt failed because the security layer encountered a processing error during the first negotiations with the remote computer”.
- The L2TP-based VPN client (or VPN server) is behind NAT.
- A fake certificate or pre-shared key is placed on the VPN server or client.
- The trusted machine certificate or root machine certificate is not present on the VPN server.
- The machine certificate on the VPN server does not have ‘server authentication’ as EKU.
How to Fix “The L2TP connection attempt failed because the security layer encountered a processing error during the first negotiations with the remote computer”.
Restart your VPN network adapter.
- Right-click on’Start’ and click on’Device Manager’.
- Locate’Network Adapters’ and click on the drop-down menu to expand the list.
- Find your’Network Adapter’.
- Right-click on it and select Uninstall.
- Now click on’OK’.
- Reboot your system.
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Changing IPSEC parameters
- Open the Administration Tools from the Control Panel.
- Double-click on Services.
- Search for IPSEC services. (ike and AuthIP IPsec Keying Modules,IPsec policy agent) Confirm that the start type is automatic and that the status is set to Start. If necessary, double-click on IPsec Services to change these settings.
- If it is not “started”, right click to start it.
- Right-click and select Properties. For “Start type”, select “Automatic” and save.
- Test the VPN connection.
- Restart the VPN connection and test it.
Activation of MS-CHAP v2
- Make sure that the VPN connection is correctly configured to match the identification information of the VPN server to which you are trying to connect and add the connection.
- Once the connection is added, it will appear in the list of network adapters.
- Press Windows + R to open the Run command prompt.
- Type “ncpa.cpl” and press “Enter” to open the network adapter settings.
- Right-click on the added “VPN” connection and select “Properties”.
- Click on the “Security” tab and activate the “Allow these protocols” option.
- Activate the “Microsoft-CHAP Version 2” option and click on “OK”.
- Try to connect to the VPN and check that the problem persists.
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CCNA, Web Developer, PC Troubleshooter
I am a computer enthusiast and a practicing IT Professional. I have years of experience behind me in computer programming, hardware troubleshooting and repair. I specialise in Web Development and Database Design. I also have a CCNA certification for Network Design and Troubleshooting.