that you installed the drivers for it!!!
For USB you normally have to install the drivers FIRST before plugging the printer in and turning power on.
Have Win 98 SE and printer shot craps. I installed an Epson C-80 spare and had in on USB. Got the "not printing to valid port" message and re-installed with parallet cable and moved configuration to LPT1 but still get the same message. Everything is plugged in and the printer is on. How do I check to make sure that the printer is printing to a valid port? Thanx