Question : Port 10000 w. NT4.0SP5

I have a WINNT4.0SP6a running a client/server accounting package(specifically Mas90(www.sage.com)) This host is set to communicate(and accept requests) on port 10000. The trouble we're having is getting a client(Winnt wkst 4.0sp5) to connect from a remote location. All local connections from clients go through just fine. The difference is that other clients are connected via a 10Mbps lan, and this remote client has to go through a 56K DDS line before getting to the server. Funny thing is everything else works fine(even regarding netbios issues) I'm currently "on the phone" with their tech support, but I was just wondering if it could possibly be either a service pack issue, or possibly a general WinNT issue(is port 10000 reserved for something else, or restricted in any way?
I've done some sniffing on the line, but it doesn't tell me much. It just seems that the packets are not getting through. Our routers are RH Linux 6.x ones, and I hesitate to question those, since everything else goes through. On the same issue, there is no firewall between the two locations.
Please help.
Thank you.

Answer : Port 10000 w. NT4.0SP5

Sounds like NAT is the culprit.  VPN will fix!  I have pop up my VPN connection at home before running Mas90 because I run NAT.

>What I mean is that if I check the "in use" on the server it does not list this client or username

It is strictly a Sockets app.  It does not use NT securitiy or NetBIOS whatsoever.  You are just opening a port on the server and remote controlling a PVXWIN32 interpreter.

>Does mas90(client server version) run on a modem(28.8) connection? and how well?

It will work OK for inquiry and light data entry, but if you try to print reports or forms using the Crystal engine, you won't be pleased.  Cystal requires "file" level access while canned Mas90 reports do not.