Mine said the same thing about the flash disk not having enough space to copy the backup files, which is why I unmounted and reformated/repartioned the flash disk. After that, I tried copying again, and all was good.
How do you unmount the flash disk?
There is something in the control panel, I don't remember off the top of my head, but it is something that manages the disks. You can't format/repartition unless you unmount it. Then after its unmounted, you can delete it, then recreate it and repartition it. Make sure you do the 1.xxGB one, and not any of the other ones.