TCP/IP and programming connectivity problem (routing table question)

Folks,

I didn't know which list would be more appropriate, so I have sent it to
both above. Apologies if one or the other is not suitable. 

My problem is that I have written a set of RPG ILE service programs on the
AS/400 and a Delphi Server application on the PC. At one client site the
AS/400 can communicate perfectly with the Delphi TCP/IP server when I am on
site. When I connect over a VPN, I get a different network address (which
does not appear in the TCP/IP routing table on the AS/400) and the
communication no longer works.

I am now trying to setup the same programs on another site, and the service
program to PC communication is acting the same (ie. no traffic to the PC).

My question is, are routing table entries on the AS/400 necessary to
communicate with particular PC network address ranges (kinda like acting
like an outbound firewall).

Am I making any sense at all ?

Thanks in advance,
Darren McBride