Windows will often move USB/Serial port assignments like musical-chairs. IE: If you boot Windows with a a USB laser printer ON, and a color inkjet printer ON and a WEB camera ON then turn your scanners and get it all working, then restart Windows with one or some of those other devices OFF the your scanners will end up on other emulated USB/Serial ports and you will need to reconfigure the software for the new port assignments the scanners now reside on. This is a real pain in the butt if you're constantly moving things to different ports, connecting, disconnecting, turning them ON & OFF. I like the good old days when scanner used real RS232 serial ports and PC's had at least two serial ports or you added additional serial ports on a PCI card. I still have two real serial ports on my Dell Workstation and they're a joy to use!