Windows 10/L2TP post KB5009543 error 789 when connection

[JohnIreland]

Afternoon all,

Trying to connect to a customer's Meraki VPN and I get the "The L2TP connection attempt failed because the security layer encountered a processing error" when trying to connect.

In a post of 17/1/2022 it was suggest to try and 'out of band' Microsoft cumulative fix to Windows 10 Pro 21H2/Build 19044.1706, however this (KB5010793) is not applicable to my PC as it has had subsequent cumulative fixes since then - crucially excluding the one in which a fix for this issue was included.

Also, as the PC was built after KB5009543 was released, there's no option either through Windows Update Settings or the command line to uninstall this KB.

Therefore, the fix posted by MarkChan on 17/1/2022 needs an update - is there a current updated fix for this for PCs where this is still an issue after current cumulative updates have been applied?

Cheers,

John

[Brash]

You're correct that the error "The L2TP connection attempt failed because the security layer encountered a processing error" was symptomatic of the bad update Microsoft pushed on January.

However of you've ruled that out, it's likely that the error is indicative of a connection/configuration problem. Typically when seen it's due to CHAP and/or PPP settings incorrectly configured.

I suggest checking the configuration against the following: https://documentation.meraki.com/MX/Client_VPN/Client_VPN_OS_Configuration#Windows_10

[JohnIreland]

Yes - done all that and re-checked it this morning. Indeed I had to resolve this same issue on an older PC when it first arose - that had the advantage that the offending KB was there to be uninstalled.

This is a screenshot of attempting to connect this morning -

[ClaytonDaniels]

@JohnIreland Did you ever resolve this issue? I'm experiencing the same issue after some Certificate mishaps and looking for some advice!

Thanks,

-ClaytonDaniels

[Mack023]

I have solved my issue by uninstalling latest security updates.