We have the following setup:
A Digi EL-32 (this is a 32 port serial port server) which is connected to the network. On one of the ports of the port server is connected a US Robotics I-Modem (ISDN & V.34). On my NT Workstation machine I've set up the software for the port server, installed the drivers for the modem and set up dialup networking.
All this works fine. The problem is that when I try to connect to the ISP, I get the "Verifying username and password" bit, and then immediately after that I get "Error 629: Port was closed by remote machine"
I suspect it may have something to do with IP adresses, but I'm not sure what to look for or how to set this up.