3 dedicated nics on server 2k3

I’ve setup a domain as the company is making use of the service of 2 ISP they wanted to keep there VPN and NAT separated from each other.

So I’ve configured a 2k3 RAS member server with 3 nics.
1 nic for the VPN connection
1 nic for NAT
1 nic for LAN

The problem that occured is that the VPN connection is working but, the moment I put the NAT connection the VPN drops.

The VPN connection is running directly on a public IP address and the NAT is running trough DSL (private IP address).

The Domain has it DC, DNS.

Is there any suggestion?