Hi, QCBN.
I never did get a resolution to the problem. The best "support" I could get was that NCH doesn't actually recommend the use of any make of voice modem with IVM So, what I did was: I upgraded to 5.04 and I trashed the modem and went for VoiP. And I bought a support package, which went against the grain because I have always felt that when you buy a software package you should at least get enough support with it to get the thing working!
VioP wasn't a walk in the park to get up and running but I did eventually succeed and now that it is working, it seems to do so very well.