Today one of my clients was unable to connect to VPN with the following error: “The L2TP connection attempt failed because the security layer encountered a processing error during initial negotiation with the remote computer”.
After verifying that all L2TP VPN connection settings are correct, I discovered that the problem occurred after updating KB5009543 on Windows 10 or KB5009566 on Windows 11, as reported by many users on the Microsoft Q&A forums.
How to fix: Updates KB5009543 and KB5009566 break L2TP and IPSec VPN connections. *
* Update (January 18, 2022): According to Microsoft, the issue is fixed in KB5010793 for Windows 10 and KB5010795 for Windows 11. So, proceed to download and install the appropriate update from the Microsoft update catalog and check if the issue is resolved. (if not, follow the steps below)
Step 1. Uninstall updates KB5009543 or KB5009566
1. open the Running utility by clicking the button Windows + R keys on your keyboard.
2. Type cmd and press the buttons Ctrl+Shift+Enter To open the command prompt in administrator mode. *
*Note: If you see any windows asking for permission, click on it Yes.
3. Enter the following command according to your operating system and click Enter:
- wusa / delete / kb: 5009543
- wusa / delete / kb:5009566
4. When the confirmation dialog box appears, click on it Yes.
5. After the deletion process is complete, restart turn on the computer and try to connect to the L2TP VPN. Usually, the problem needs to be solved. *
*Note: If the problem persists, follow the instructions in the following article: FIX: Unable to connect to L2TP VPN on Windows 10
Step 2. Avoid reinstalling updates KB5009543 and KB5009566.
Now go ahead and prevent reinstallation of KB5009543 or KB5009566 using the Show/Hide Updates utility.
1. Download the Tool to show or hide updates tool: https://www.majorgeeks.com/files/details/wushowhide.html
2. Running Click “wushowhide.diagcab”. The next one and then press Hide updates.
3. select the 2022-01 Cumulative Update for Windows 10 (KB5009543) or 2022-01 Cumulative Update for Windows 11 (KB5010795) and press The next one.
4. When the operation is complete, press Termination and keep up the good work!
That’s it! Let me know if this guide helped you by leaving a comment about your experience. Please like and share this guide to help others.