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.
You log into your windows computer and try to establish the vpn connection only to get the error can’t connect to vpn the l2tp connection attempt failed because the security layer encountered the processing error during initial negotiations with the remote computer i assume that everything is okay with your vpn connection and it was working before just fine the problem with something suddenly stopping working in windows is most probably related to some buggy windows update i am not in the mood to hunt which particular update has caused the issue so we’ll fix it in another way i will be demonstrating the solution in the latest and so-called greatest windows 11 but the solution will be the same in windows 10 and most probably in windows 8 and 7. this bug usually affects connection that uses l2tp protocol ipsec iq protocol or just plain ipsec and the problem is with ipsec to try to fix it launch windows registry editor and go to this location
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Rasman\Parameters
here you will need to change the settings of two parameters if they exist and if they do not exist you will have to make them and change the settings in this example the first parameter exists and it is called allow pptp weak crypto
AllowL2TPWeakCrypto = 1
by default it is set to 0 that means it is disabled try changing the setting to 1 thus enabling this feature reboot your pc and try to connect to your vpn if the error persists go back to the same location in register editor switch this parameter back to 0 and change another parameter in this case it does not exist so we have to make it right click on an empty spot and create a new d word 32-bit value give it a name prohibit ipsec keep in mind that it is ipsec not lp sec
ProhibitIpSec = 1
after you created this parameter leave it 0 reboot your pc and try to connect to your vpn if that fails change this parameter from 0 to 1. that will disable ipsec for your l2tp connection so in case your vpn forces that you will not be able to connect however in many cases l2tp is only used to authorize the users and not to create an ipsec connection and in this case setting this parameter to 1 may help you resolve the issue try playing around with those two parameters having them both at 0 both at 1 or 1 at 0 the added 1 and vice versa don’t forget to reboot after each change of the parameters and with lock that will fix your vpn issues
Download .reg file to import to Windows registry – click here