Please copy the bcd file to your USB HDD, this should solve the issue. Probably the Flash drive drive is too slow?
USB drives smaller than 2GB cannot be used with uTrack24.
If you still not able to update you can use the bcd file with network update method as well. https://cymaticaudio.com/images/downloads/manuals_and_brochures/uTrack24_FirmwareUpdate_EN.pdf