First run seems successful.

Of course, you'll want to test this on your own.

** If you installed from ports, you can use this updater. If you installed the Plex plugin, **
** this is not the script you're looking for **

How to use:
SSH to the FreeNAS box.
run jls and get the ID of the Plex Media Server jail
jexec csh
sh plexupdate.sh

If all goes well, the install will be successful.

Good Luck!