FORTIGATE 200 PORT FORDWARDING DNS PROBLEM

Archived from groups: comp.security.firewalls (More info?)

I have a problem with a Fortinet Fortigate appliance.

In the local network there is a Windows 2000 Server machine runing DNS
server and IIS with a local IP 192.168.10.7 ( hosting a website) this
machine is at a DMZ behind a Fortigate 200 Firewall, and is reachable
from the internet using "Static Nat" from a public IP to the internal
IP of this Windows Server.

I recently install a new Linux machine on the same LAN with IP
192.168.10.10 running Apache on default port 80 running a website and
want this website can be viewed from the internet, so i tought that
port redirection was the solution and setup a "Port Forwarding" rule on
the Fortigate opening a 8088 port on external that redirects to the
internal ip ( 192.168.10.10 ) on port 80 ( http ).

Unfortunately we have just only one public IP , and the port
redirection did not work, may be because the "Static Nat" that makes
work the website on the windows box supersedes the Port Forwarding
rule.
So I disable the Static Nat to the Windows box and create Port
Forwarding from external to ports 80tcp, 53tcp, 53udp. My linux site on
port 8088 works, the windows site works ... but after a time the Domain
Name that the Windows serves goes down from Internet. When I enable
NAT again to the Win box, the DNS works again!.

What i´m doing wrong?.