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

You may come across an error “The L2TP connection attempt failed because the security layer encountered a processing error in Windows 10 or Windows 11” when you try to make a VPN connection. L2TP is a well-known connection used for encryption and protection of VPN. It is a sought-after VPN with the Layer 2 tunnelling protocol that bypasses the security restriction of a particular area. But sometimes you may face the “Can’t connect to VPN. The L2TP connection attempt failed because the security layer encountered a processing error during initial negotiations with the remote computer” error. The reasons could be when the Microsoft CHAP v2 protocol is disabled or when the PPP settings are not configured properly. Anyways, nothing to worry about, we are providing you with some useful methods.

5 Ways to Fix “L2TP Connection Attempt Failed” Error

Turn on the Microsoft MS-CHAP v2 Protocol first.
Uninstall the latest security updates.
Try to Reinstall the VPN Network Adapter.
Active the LPC Protocol Extensions.
Try creating a new UDPE Encapsulation Registry Key.

Method 1: Turn on the Microsoft MS-CHAP v2 Protocol first:

Disabled Microsoft CHAP v2 protocol may lead to an L2TP connection attempt failing because the security layer encountered a processing error in the system. So, you have to enable it. Follow the given guidelines below:

Open RUN dialog.
Type ncpa.cpl in the given text box and hit Enter.
The Network Adapter Settings will show up.
Right-click the VPN connection.
Now choose Properties from the menu.
A new popup will float up.
jump into the Security tab.
Scroll down and click the radio button that reads Allow These Protocols.
Check the small box beside Microsoft-CHAP Version 2.
Now click OK and try to reconnect the VPN client.

Method 2: Uninstall the latest security updates:

Sometimes your latest update may bring some issues that lead to breaking your VPN connection. You can uninstall your recent update to fix your problem. Here’s how you can uninstall the latest security update.

Open Search box.
Search APPWIZ.CPL in Windows search box and click on it.
Right-click on the most recent Microsoft Windows update.
Click on Uninstall.
Restart your computer.

Method 3: Try to Reinstall the VPN Network Adapter:

Reinstalling the VPN Network Adapter may fix the L2TP connection attempt failing because the security layer encountered a processing error in Windows 10 or 11. For that, you have to reinstall the existing Driver Software from Device Manager and try installing a new one. Follow the givens steps :

Open Run dialog (Win+R).
Type devmgmt.msc in the search box.
Click OK and open up Device Manager in a separate window.
Move out for Network Adapter.
Double click the device.
Now make a right-click on your Network Adapter, once the drivers are split up.
Select the Uninstall device.
Hit uninstall again.
Restart the PC after completing the process.
Now download the compatible driver software again.
And install them in the system.

Method 4: Active the LPC protocol Extensions:

Activating the LPC protocol Extension may solve the problem you are facing. You must try to see by activating the LPC Protocol Extensions.

Know how you can activate the LPC Protocol Extensions by following our steps:

Press Win+R to open the RUN dialog box.
Type ncpa.cpl in the box and press Enter.
Locate the VPN in the Network Connections.
Right-click on it and select Properties.
Go to the Options tab and click on the PPT Settings button.
Now, check the box next to Enable LCP extensions in the PPP Settings.
Click OK to save the changes and do exit.

Now you can try connecting the VPN. Hope it will work.

Method 5: Try creating a new UDPE Encapsulation Registry Key:

Generally, when the VPN client is wrongly configured to run behind a NAT service, it often brings instability to the system. Thus you won’t be able to connect with the VPN server without any trouble. Hence you suffer the L2TP connection attempt failing because the security layer encountered a processing error in the system. In that case, you have to modify the Registry Editor keys. Go with the given guidelines below.

Open the search box and type Regedit.
Press Enter to open.
Now navigate to HKEY_LOCAL_MACHINE\ SYSTEM\ CurrentControlSet\ Services\ PolicyAgent.
After reaching to PolicyAgent, jump to the right-side panel.
Right-click on the space.
Choose New=> DWORD (32-bit) Value.
Name the new DWORD as AssumeUDPEncapsulationContextOnSendRule.
Enter the value data as 2 and press OK.
Restart the PC and try to connect the VPN again.

There might be several reasons for the L2TP connection attempt failing because the security layer encountered a processing error in the system having Windows 10 or 11. After doing many case studies we have provided you best 5 methods to solve the mentioned problem in Windows 10 or 11. We hope it will work for you.

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