Fix The L2TP Connection Attempt Failed Because The Security Layer Encountered A Processing Error

The L2TP connection attempt failed because the security layer encountered a processing error
The L2TP connection attempt failed because the security layer encountered a processing error

There’s a chance you’ll run across a mistake while trying to connect to a VPN in Windows 10 or 11. You will get the error message, “The L2TP connection attempt failed because the security layer encountered a processing error” L2TP is a well-known VPN connection that encrypts and protects data.

It’s a popular VPN that uses the Layer 2 tunneling protocol to get around a specific area’s security restrictions. However, you may occasionally see the error “Can’t connect to VPN.”

Since the security layer encountered a processing problem during initial discussions with the remote computer, the L2TP connection attempt failed.” Anyway, don’t worry; we’ve provided you with helpful techniques.

What is the L2TP Connection?

Layer 2 Tunneling Protocol (L2TP) is a tunneling protocol used in computer networking to support virtual private networks and ISP service delivery. It just encrypts its own control messages and offers no encryption or content confidentiality.

Instead, it provides a tunnel for Layer 2 communication (which can be encrypted) to be sent over a Layer 3 encryption protocol like IPsec. However, in Windows 10 or 11, the L2TP connection attempt may fail because the security layer encountered a processing issue.

When a user attempts to connect to a remote VPN server, the security layer encounters a conflict, resulting in VPN error 789. When a user attempts to start a new client session using Windows 2000 terminal service, the L2TP connection attempt fails because the security layer encountered a processing error.

The error could be caused by a problem with the computer or the VPN itself. Furthermore, the Operating System settings for using the L2TP VPN may be incorrect, resulting in the connection ending locally even before it begins.

Fix The L2TP connection attempt failed because the security layer encountered a processing error

After receiving numerous reports from diverse individuals, we decided to study the issue and devised a series of solutions to resolve it. We also looked into the reasons for it being activated and came up with the following list:

  • Disabled Protocols: The error may occur if the Microsoft CHAP v2 protocol is disabled in the VPN Connection’s properties. Most VPN connections will not work unless this protocol is enabled.
  • PPP Configuration: The Point to Point protocol must be correctly configured before users attempt a VPN connection. This protocol includes an LCP protocol with some additional extensions that must be enabled for the connection to work correctly.

We’ll move on to the solutions now that you have a fundamental knowledge of the problem’s nature. To avoid conflicts, make sure to implement these in the order they are stated.

1. Enable the Microsoft MS-CHAP v2 Protocol

To get the VPN up and running, you must have the Microsoft CHAP Version 2 (MS-CHAP v2) activated on Windows. As a result, it is critical to check if it is enabled and, if not, to enable it.

Step 1: To open the Run command window, right-click on the Start menu and select Run.

Step 2: The Run dialogue box will appear.

Step 3: Next, type ncpa.cpl into the Run dialogue box and click OK.

Step 4: The Network Connections window will now appear. Right-click the VPN connection and choose Properties from the drop-down menu.

Step 5: Switch to the Security tab in the VPN properties window.

Step 6: Allow these protocols to be used is now enabled. Also, enable Microsoft CHAP Version 2 (MS-CHAP v2) by checking the box.

Step 7: Finally, press OK.

After that, try connecting to the VPN again to check whether the error persists.

2. Uninstall the latest security updates.

Your most recent upgrade may cause some troubles, resulting in the loss of your VPN connection. To resolve the issue, remove the most recent update. Here’s how to remove the most recent security update.

Step 1: Start typing in the search box.

Step 2: In the Windows search box, type appwiz.cpl and press Enter.


Step 3: Select the most recent Microsoft Windows update by right-clicking on it.

kb:5009543 for Windows 10

kb:5009566 for Windows 11

Step 4: Next, choose Uninstall.

Step 5: Finally, restart your device.

3. Reinstall the VPN Network Adapter.

Many situations show that problem of VPN 789 arises in a system due to network adapter instability. As a result, receiving the essential data for initialization becomes tricky for the VPN server. Frequently, merely reinstalling the Network Adapter driver reduces the problem.

Because the security layer in Windows 10 encountered a processing problem, the L2TP connection attempt failed. Go to Device Manager and delete the existing Driver Software before installing a new one downloaded from the internet. Here’s how to go about doing it:

Step 1: Using the Win+R hotkeys, open the Run dialogue box.

Step 2: In the Run dialogue box, type devmgmt.msc.

Step 3: Open Device Manager in a new window by clicking the OK button.

Step 4: Double-click the Network Adapter on the left side of the screen.

Step 5: Right-click on your Network Adapter after the drivers have been split up, and then finally, select the Uninstall device.

Uninstall device

Step 6: Restart Windows after clicking Uninstall

Step 7: Return to the previous session, open a web browser, go to the manufacturer’s website for driver software, and download the compatible one.

Step 8: Install the file on your computer.

4. Activate the LPC Protocol Extensions.

Configuring the PPP (Point to Point Protocol) parameters to allow LCP extension is an essential operation. The system may have been disabled due to third-party software or human error and is now giving away information. The L2TP connection attempt failed. We can easily enable it by following the steps mentioned below:

Step 1: Choose Run by pressing the Win + X keys.

Step 2: In the provided box, type ncpa.cpl and click OK.

Step 3: Right-click on the VPN connection in Network Adapter Settings and select Properties.

Step 4: Select the PPP Settings button from the Options tab.

Step 5: Select the Enable LCP Extensions option. To save the changes, click the OK button.

Select the PPP Settings

Step 6: Connect to the VPN server again to see if the problem has been repaired.

5. Try to create a new UDPE Encapsulation Registry Key.

The system can become unstable when the VPN client is misconfigured to run behind a NAT service. As a result, you won’t be able to connect to the VPN server without difficulty.

As a result, the L2TP connection attempt fails because the security layer encounters a system processing problem. You’ll need to change the Registry Editor keys in that instance. Follow the steps outlined below.

Step 1:Type regedit into the search box.

Step 2: Then, press Open.

Step 3: Next, go to HKEY_LOCAL_MACHINE > SYSTEM > CurrentControlSet Services PolicyAgent.

Step 4: Then, jump to the right-hand panel once you’ve arrived at PolicyAgent

Step 5: Next, right-click on the empty slot.

Step 6: Select New DWORD (32-bit) Value from the drop-down menu.

Step 7: Name the new DWORD as AssumeUDPEncapsulationContextOnSendRule.

Step 8: Enter two as the value data and click OK.

Step 9: Restart your computer and attempt connecting to the VPN again.

6. Recreate IPSec Services

The reason for the failure of the L2TP connection could be that the IPSec services are experiencing some form of issue or glitch. In this instance, you might consider restarting your PC’s IPSec services.

Step 1: Seek and open Services. You can also use the Run dialogue box to type services.msc.

open services

Step 2: The Services Manager window will now appear. Look under the Name column for the IKE and AuthIP IPSec Keying Modules and double-click it.

Step 3: Ensure that the Startup Type is set to Automatic in the IKE and AuthIP IPSec Keying Modules Properties box.

Step 4: To halt the service, click the Stop button, and then, to restart it, click the Start button.

Step 5: Next, click the OK button.

Startup Type Automatic

Step 6: Open the IPSec Policy Agent service in the Services Manager window and follow the same instructions as before.

You’ve now successfully resumed the IPSec services, and you may try restarting your VPN connection, which should now be up and running.

7. Verify the Certificate Placed on the VPN server

When an incorrect certificate or a previously shared and poorly configured key is used to connect to a VPN server, the security layer may encounter a processing problem. The L2TP connection attempt failed because the security layer encountered a processing error.

As a result, it’s critical to double-check that the Certificate you’re using is correct and valid. At the same time, a unique and adequately configured key must be set on the client or VPN server end.

By validating the identical credentials on the client-side and VPN operator, you can certainly use a Pre-Shared Key (PSK). To avoid the L2TP connection attempt failed because the security layer encountered a processing problem in Windows 10 or 11, be highly cautious before installing them.

Final Words

So, these were the options for troubleshooting the “The L2TP Connection Attempt Failed Because the Security Layer Encountered a Processing Error” problem on your Windows 11 or Windows 10 system.

We hope that our troubleshooting tutorial was helpful to you in some manner. Since the disabled MS-CHAP v2 or LCP extensions prevent the VPN from establishing an L2TP connection in the majority of circumstances, Methods 1 and 2 should be enough to resolve the error.

To avoid software conflicts, you can also try restarting the IPSec services, reinstalling the VPN network adapter drivers, and removing the most recent security update.

Posted by
Ratnesh Kumar

Hi Everyone, I am Ratnesh Kumar. Currently, I am running a Media company called Yorker Media. Under the Yorker Media portfolio, we have five Tech Websites targeting global audiences and several websites for our Indian audiences. Combining all those websites, we are getting close to 300k visits a month. It all started in 2017 when I started my YouTube journey as a Tech content creator. At the same time, I also learned about Blogging and started a blog as an extension of my YouTube channel. So, after hustling for over a year, I quit individual content creation and moved to the tech media business. I started my first project in the industry, TechYorker.Com. Initially, I needed more funds to run the business. So, to arrange funds, I started working as a freelancer. After almost five years, I have experience with growing a Digital Media business, and Freelancing. I have planned to create content around the skills and knowledge I have gathered in the last few years. Thank you!

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