To me, this really sounds like a BIOS disk geometry problem, which was quite common when moving disks or making controller changes many years ago. I was vaguely impressed when I learned that the FreeNAS team had been shipping disk images rather than using an installer (the so-called "installer" is merely a disk-image-writing wrapper) because my impression had been that this was a non-fixable issue... but I had never really investigated exactly how a BIOS would implement this for a flash drive. I kind of wrote it off as someone having fixed the painful-stupid of C/H/S.
Anyways, it appears to me that FreeNAS is built with a disklabel of */255/63; an older FreeNAS system here reports
parameters extracted from in-core disklabel are:
cylinders=967 heads=255 sectors/track=63 (16065 blks/cyl)
If you were to get a FreeBSD install disk and install the smallest possible system onto your flash drive, my guess is that your system might prefer a */16/63 or some other odd geometry. Or possibly maybe there's none at all that works, because sometimes manufacturers forget to test "odd" features like flash drive booting.