VPN

hi all
I've a problem with PPTP VPN login
it's work fine for LAN clinets, but i can't login from WAN.
i've 3 interface:
RED - WAN 192.168.168.1
GREEN - LAN 192.168.0.1
ORANGE - DMZ 192.168.1.1
server PPTP 192.168.168.100
Can anyone help me?

if you want anything more than a wild ass guess, you need to give us a little more detail than that.

BTW, we don't call them "Red" "Green" and "Orange" here.   

CS...

if you want anything more than a wild ass guess, you need to give us a little more detail than that.

sorry for my poor english
i've connected a XP client (configured on 192.168.168.100 PPTP server) on WAN interface and it doesn't login. I'don't know why...
Other Xp clients (configured on 192.168.168.100 PPTP server) on LAN interface work fine.
i don't know what other detait i must give us.

BTW, we don't call them "Red" "Green" and "Orange" here.   

why?