Using XP built-in VPN Client

Hello,
I have a FortiGate 60 router that I configured to work as a VPN server.

I would like to connect to this VPN server using XP built-in VPN Client (from network connections), but it's not working.

In the XP VPN Client, I have configured in IPSec the preshared-key, but it fails on the part of "authenticating username and password".
I'm not sure what should I write in the XP VPN client as username/password, since in the VPN server i have only the general name for the service, and the preshared-key. So I tried to leave the username/password blank but it's not working.

Please help,
Yoav