This can happen if you unplug the programming cable from the USB port after every time you download a program. The programming cable was designed to be disconnected from the robot side of the cable, not the USB side. You should leave the USB side of the programming cable connected to your PC. If you are having a hard time downloading programs to your robot, it could be a USB problem. Disconnect the programming cable from your computer and restart the computer. Once the computer is up, reconnect the USB adapter.