Connection Troubles - FM Server 5.5. OS X

[basd]

I am trying to connect to a remote Filemaker database with no success. I can connect to other people's FM Servers from this location, but there is one giving me trouble. Problem is, other people are able to connect to it.

- the FM Server in question is running on an OS X machine (Jaguar running FM Server 5.5) behind a firewall with TCP/IP and UDP traffic on port 5003 being forwarded to the machine running the server

- I can see the hosted database from many external locations on both mac and pc versions of FM Pro 5.5 or 6 - but not from some locations

We have also tried the IP Address followed by ":5003" without success.

Does anyone have any ideas? Other than making sure that port 5003 is properly routed, is there anything else that needs to happen on the hosting end?

Thanks....