Hi,
Can you please verify the size/formatting of the USB drive? I would try both FAT and FAT32
https://kb.juniper.net/InfoCenter/index?page=content&id=KB31622
Alternately you could run a TFTP daemon on the laptop connecting to the firewall:
https://kb.juniper.net/InfoCenter/index?page=content&id=KB20643
I hope this helps. Regards,
Nelumbo