I’ve just upgraded to 2.4 Beta, and the USB Rom-transfer no longer works. I plugged in my old stick to transfer back all my old ROMS, but nothing happened, so I figured 2.4 might use a different layout, so I copied the roms to my PC, formatted the thumb drive, then put it back in the Pi. It still didn’t work, so I did a bit of troubleshooting on my own. It is showing up correctly in the list of USB devices as a mass storage device, so it’s reading it fine. I then went into retropie_setup.sh and went through the USB service setup. I got the normal Installing… Configuring… and then it finished. However, it still did not work. I have restarted the Pi several times and I still have a blank thumb drive.
The only thing I can think of that I made a mistake with was not updating the retropie setup script first. When I fixed it I updated the script first, rebooted, and then went back into the setup script and installed the usbromservice