Ted, if you provide some more information it would help in finding a
solution your problem.

First, what is the make and model of both the computer and the
USB-serial converter? Second, what operating system are you using (XP,
NT, 98, DOS)? Third, if Windows, have you tried the standard Windows
tricks of looking for hardware conflicts, changing the serial port the
USB-serial adapter is on, setting baud rates, etc.? Fourth, if Windows,
what are the values that have been set by the installer for com number,
bps, data bits, parity, stop and flow control? Fifth, have you tried
booting into a pure DOS environment and using Data-cam with a fully
qualified command line to specify file name and com port?

I'm using an IBM T42 notebook with an IO Gear USB-serial adapter, and
I've had zero problems talking to a Cambridge Model 10 under XP and 98
using SeeYou, Data-cam and Vali-cam. This setup also works well under
DOS using Data-cam and Vali-cam.

So, as you no doubt suspected, it can be done! Taking a wild guess, I
suspect that your problem lies in getting the com port of the
USB-serial adapter to be com 1 or com 2. Most of the time the installer
puts them way up high, and this can lead to trouble (depends upon the
BIOS and the OS).

-John