localhost is what it says. This domain name is a loopback to IP address 127.0.0.1, which is not routed. See http://en.wikipedia.org/wiki/Localhost for more details.
From external clients, you need to specify the DNS name or DNS alias name (prefered) or the IP address (not recommended) of your web host, eg. http://www.mydomain.com/fmi/iwp
Thanks for your answer.
I know what localhost is, thank you. My problem is router related, I think I forgot to add the port forwarding from Internet to the IWP.
After contacting the support it seems that the problem is coming from my company's network, we're using a Windows SBS to host our Sharepoint and some folks at fmforums.com are saying that it's not possible to have those 2 servers on the same network.
I'll check with my network admin to disable it for 5 minutes just to do some tests.
The problems was from our Windows SBS on the same network, the Sharepoint installed on it is taking over the IIS of FileMaker.
I made some test by re-routing the HTTP flow toward the IP adress of my IIS.
Problem solved !