I have a Vigor2860Vn+ running firmware version 3.7.8.

I've followed the advice given to set up a L2TP VPN from a Windows 7 machine to the Draytek...

http://www.draytek.com/index.php?option=com_k2&view=item&id=2771&Itemid=293&lang=en

However after about 15 seconds of trying to connect I receive the following error on the PC...

Error: 789 "The L2TP connection attempt failed because the security layer encountered a processing error during initial negotiations with the remote computer"

In the web interface "Syslog Explorer" I see "Responding to Main Mode from xxx.xxx.xxx.xxx"

Can anyone help with this? I notice others have seen issues but these were supposedly resolved in firmware 3.7.8.

I got the error again but track it down.
I reread http://www.forum.draytek.co.uk/viewtopic.php?f=8&t=19266, and I then had the idea to deactivated all my LAN-LAN VPN.
I found that on of my VPN LAN-LAN when activated generated the issue. On Win7 it is 789, on Win8 it is 789 or 868. I deactivated it as it was just for tests.

There are possible other issues with Win7. I can't remember what I done in registry/policy or KB applied and if it was needed.
My present firmware is 3.7.8.1