@cmb:
Sounds like the same issue FreeNAS folks appear to have tracked down to:
https://bugs.freenas.org/issues/3273
at least starting from the mountroot failure "failed with error 19" and following the trail lead there.
Are you booting from a USB drive of some sort? What are the details of your hardware?
I've seen that this was already been more than few months old, but if somebody out there still encounter this probel, you can try my solution below.
I was able to resolve this issue with my pfsense 2.3.2 on Windows 2012 R2 Hypver-V.
mountroot> mount <enter>Expected sample output:
/dev/57c0727e81075d96e on / (ufs, local, journaled soft-updates)
devfs on /dev (devfs, local)
/dev/md0 on /var/run (ufs, local)
devfs on /var/dhcpd/dev (devfs, local)
Take the first line as your mountpoint
mountroot> /dev/57c0727e81075d96e <enter>Expect the machine to continue boot process.
Cheers!!!</enter></enter>