FIX: Windows 10 VPN error 789 connection failed due to security issues

Milan Stanojevic
by Milan Stanojevic
Deputy Editor
Milan has been enthusiastic about PCs ever since his childhood days, and this led him to take interest in all PC-related technologies. Before joining WindowsReport, he worked as a front-end web developer. Read more
Affiliate Disclosure
  • VPN error 789 appears when a Windows 10 system isn't configured properly and it is connected to a VPN using the L2TP protocol.
  • This error can be fixed with a quick network adapter reset and a certificate check. IPSec configuration should be changed as well as a fallback solution.
  • If you are interested in VPN protocols, check out our encryption section on the website to learn more.
  • Visit the VPN How-to Guides for articles that instruct you on how to get the most out of your VPN.
FIX: Windows 10 VPN error 789 connection failed due to security issues

If you’re using a VPN, and get prompted with the Windows 10 VPN error 789 that states:

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

This error pops up when your system is not properly set up to connect to an L2TP server, thus the connection attempt fails even before you establish a connection with the server.

It is also linked to the incorrect configuration of your operating system like Windows 10 in this case. This generic error is thrown when the IPSec negotiation fails for the L2TP/IPSec connections.

Other possible causes include:

  • L2TP based VPN client (or VPN server) is behind NAT.
  • Wrong certificate or pre-shared key is set on the VPN server or client
  • A machine certificate or trusted root machine certificate is not present on the VPN server.
  • Machine Certificate on VPN Server does not have ‘Server Authentication’ as the EKU

Here are solutions you can use to fix Windows 10 VPN error 789 on your computer.

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How do I fix Windows 10 VPN error 789?

  1. Reset network adapter
  2. Check the certificate
  3. Re-enable IPSec on your computer

Before trying any of these solutions, ensure that L2TP and IPSec pass-through options are enabled from your router. If you configured your VPN service manually, then make sure you use the preshared key 12345678.

Additionally, you should consider changing your VPN provider.

Since you have already encountered errors with your previous service, you will probably be looking for one that is stable and secure and has no compatibility issues with Windows 10.

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1. Reset network adapter

  • Right-click Start and select Device Manager

 Windows 10 VPN error 789

 Windows 10 VPN error 789

  • Identify your network adapter and right-click on it then select Uninstall
  • Click OK
  • Restart your computer. The device will reinstall and should reset it to default settings

If this doesn’t fix Windows 10 VPN error 789, try the next solution.

2. Check the certificate

Ensure the correct certificate is used both on the client and the server-side. In case Pre Shared Key (PSK) is used, ensure that the same PSK is configured on the client-side, and the VPN server machine.

3. Re-enable IPSec on your computer

  • Right-click Start and select Run

 Windows 10 VPN error 789

  • Type services.msc
  • Find IKE and AuthIP IPSec Keying Modules

 Windows 10 VPN error 789

  • Find IPSec Policy Agent

 Windows 10 VPN error 789

  • Check the status. If it says started click to restart. If the started option is disabled, enable it
  • Double click on each of the two
  • Select Startup type

 Windows 10 VPN error 789

  • Change it to Automatic

 Windows 10 VPN error 789

  • Save the changes
  • Restart your VPN service

Once you have done all the steps above carefully, the VPN should work smoothly as the protocol settings have been reset to default.

If, however, it doesn’t work, you have to manually set the encryption method both for the server and the client-side, in order for them to be compatible.

In case you have a user-specific issue on your computer yet you still get Windows 10 VPN error 789 after trying any of the above solutions, you can also contact the customer care or tech support team for your specific VPN provider and share the details for further assistance.

Maybe it’s time for a new VPN! Choose the best tools to protect your privacy from our list!

Do let us know if any of these solutions fixed the Windows 10 VPN error 789 by leaving a comment in the section below.

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Frequently Asked Questions

  • The ports you need to open are 500 and 4500 for UDP. Check out the complete guide on unblocking L2TP for other ports and more.

  • L2TP stands for Layer 2 Tunneling Protocol and is considered better than PPTP. It secures the traffic passing by it in an IPsec tunnel. The traffic itself is not encrypted.

  • By resetting the network adapter or setting the firewall to allow traffic through port 500. More details in this article.

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