信息来源：
http://support.microsoft.com/default.aspx?scid=kb;en-us;326751
This article was previously published under Q326751
On this page
SYMPTOMS
CAUSE
RESOLUTION
MORE INFORMATION
STATUS
REFERENCES
APPLIES TO
SYMPTOMS
When you try to use a virtual private network (VPN) connection through a Microsoft Windows 2000 Terminal Services client session, you may receive the following error message:
Error: 789 "The L2TP connection attempt failed because the security layer encountered a processing error during initial negotiations with the remote computer"
However, you can successfully establish the VPN connection from the Terminal server console.
CAUSE
This issue may occur if both of the following conditions are true: • You establish a client session by using Windows 2000 Terminal Services.
• You try to establish a VPN connection by using Layer Two Tunneling Protocol (L2TP) from the Terminal server to connect to a Windows 2000 Server-based computer that is configured as a VPN server.
Back to the top
RESOLUTION
To resolve this issue, you can use a preshared key on both ends of the VPN connection. The L2TP/IPSec feature supports gateway-to-gateway VPN implementations by using a preshared key for Internet Key Exchange (IKE) authentication.
Note Microsoft does not support or recommend the use of a preshared key for IKE authentication on remote access L2TP/IPSec client connections. However, Windows 2000 is compliant with IKE Request for Comments (RFC) 2409.
Back to the top
MORE INFORMATION
To implement the preshared key authentication method for use with an L2TP/IPSec connection, follow these steps: 1. Add the ProhibitIpSec registry value to both Windows 2000 Server-based endpoint computers, and then restart both computers.
2. Manually configure an IPSec policy on both the Windows 2000 Server-based computers before you try to establish an L2TP/IPSec connection between them through a Terminal Services client session.
