If your Garmin express download fails, follow these steps, it may help:
Try by attaching the device with a different USB cable.
Try by attaching the device to a different USB port on the computer.
Check the system is connected to a power source.
If using an SD card, try formatting the SD card or try using a different SD card if one is available.
Check the Garmin Mass Storage Device for Errors.
Restart the computer/laptop.