Hi
I don't fully understand your environment.
I'm presuming the USB printer is actually a Serial printer with a USB interface? and, the printer appears as if it is connected on COM2?
Can you use the printer locally on the thin client from "com2" ?
The software that is telling you com1 and com2 are already in use - where is this software installed (on the thin client?) - maybe the thin client hardware actually has 2 on board serial ports. If so, the USB device would need to instantiate at COM3 (or later). Are you able to change that manually?
What OS is the thin client running?
cheers
peterB