How to Fix: Error 800 Windows 7 (L2TP over IP Sec Client Unable to Connect)

1. "Go to VPN Connection Properties on Windows 7, and click on ""Security"".
2. Select L2TP/IPSec for the VPN Type, and click on ""Advance"".
3. Select Use preshared key for authentication, and click ""OK"".

Windows 7 VPN Setup Wizard does not ask for the shared key when doing the setup. You need to manually input the shared key under the VPN properties. Without the shared key the VPN client wouldn’t be able to connect since our routers requires a shared key when configured for L2TP over IPSec."

Check out EnGenius Forum about similar topic: 

http://community.engeniustech.com/topic/723-how-to-fix-error-800-windows-7-l2tp-over-ip-sec-client-unable-to-connect/#comment-1892