Since the servers are decommissioned, this rarely works. However, it is worth trying first because it is the safest method.
Try a different USB cable, USB port (preferably direct to motherboard on a desktop), or reinstall USB drivers. Blackberry Z30 Firmware
If the autoloader sticks at this step, remove the USB cable, restart the computer, and run the autoloader again. Since the servers are decommissioned, this rarely works