VPN over L2TP: error 678 - one small registry key

There was a need to set up a remote access to the working computer at home (WinXP SP3). The usual thing - who does not happen.
To do this, you need to configure a VPN connection via L2TP. Also nothing special (the Internet is now directly connected to my computer, without routers, VPNs and other shamanism). All settings and keys received from the admin. I do all the letter in the letter - and in response to the error 678 - "The remote computer does not respond . "


Googled - general idea - no connection, check the firewall, wires, equipment, etc.
I tried to recreate the VPN connection, disconnect and demolish the firewall.
I read the provider's forum on the same topic - I found similar questions, but I don’t have answers and successful solutions.
I called those support provider, they say ports 1701 and 1723 are closed (and they are closed, while no one uses them). They say everything is open (and why should they close them?) All to no avail.

Then they advised to check the IPSec service - checked - turned on, loaded automatically.
')
The second common idea that is often mentioned in the internet is: install the registry key
HKLM \ SYSTEM \ CurrentControlSet \ Services \ RasMan \ Parameters \ ProhibitIpSec
equal to " 1 " - came across in solutions to the problems of L2TP connections of many providers, including my past.
I checked - I have 1. I calmed down, began to look further.
Further deaf - there were no other options.

We started to gradually start thinking about suicide reinstalling Windows, but the 7th sense said that it was a matter of trivial matters.

Began to look for all sorts of Live CD / DVD in order not to rearrange the Windows on a live computer. It turned out that in general at the moment there are no Live CD / DVDs that fully support L2TP IPSEC o_O.

One fine day, my fresh and contented head came up with the idea of ​​digging into the ProhibitIpSec key more closely - he is very suspicious - how can I prevent it from IPSec when it seems to be right? Providers do not use any encryption, but for me, for a working computer, it is just the opposite - it is very much used!
Put the value " 0 ", rebooted - and about a miracle, it earned!

Maybe for someone this decision is obvious - for me, alas, no. And none of the colleagues could not tell. As well as tech support and google. Therefore, I wrote this post.