Windows 10 Patch Tuesday in January caused “Cannot connect to VPN. The L2TP …


Microsoft’s first Patch Tuesday of 2022 seems cursed with problems. Users report that KB5009543 for Windows 10 2004, 20H1 and 21H1 is causing problems establishing a VPN connection for a number of clients and servers over the L2TP VPN protocol.

Users report that they are in the “Cannot establish a VPN connection. The L2TP connection attempt failed because the security layer encountered a processing error during the initial negotiations with the remote computer“, And primarily affects the built-in Windows VPN client when connecting to Ubiquiti Client-to-Site VPN, SonicWall, Cisco Meraki, and WatchGuard firewalls.

Microsoft has confirmed the problem with the words:

“After installing KB5009543, IP security connections (IPSEC) with a vendor ID may fail. VPN connections that use Layer 2 Tunneling Protocol (L2TP) or IP Security Internet Key Exchange (IPSEC IKE) could also be affected. “

The main workaround is to uninstall KB5009543 by going to Control Panel> Programs -> View Installed …


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