This is not exactly a "fix" yet, but I learned a workaround on the freenode Web forum
# rm /usr/local/etc/nginx/nginx.conf*
# service ix-nginx start
# nginx
Apparently there is something screwed up in the conf files, so you have to remove them first, and THEN restart the nginx process.
NOTE that the service start command returns "Failed", but this is OK. After you get this, run the nginx command (no response on the command line), and the Web GUI should be working.
NOTE I haven't tested this yet, but you will probably need to re-run these commands any time you restart the system, until the FreeNAS people come out with an update.
Not exactly an optimal fix, but at least it gets you back up and running...
