It seems to work correctly on my FreeBSD 10.2
[ghw@digitalocean.pts/0] ~/letsencrypt % ./letsencrypt-auto --agree-dev-preview --authenticator standalone --server https://acme-v01.api.letsencrypt.org/directory --rsa-key-size 4096 --email webmaster@gehaowu.com -d gehaowu.com -d www.gehaowu.com auth
Updating letsencrypt and virtual environment dependencies......
Running with virtualenv: sudo /home/ghw/.local/share/letsencrypt/bin/letsencrypt --agree-dev-preview --authenticator standalone --server https://acme-v01.api.letsencrypt.org/directory --rsa-key-size 4096 --email webmaster@gehaowu.com -d gehaowu.com -d www.gehaowu.com auth
An unexpected error occurred.
Error: serverInternal :: The server experienced an internal error :: Error creating new authz
Please see the logfiles in /var/log/letsencrypt for more details.
[ghw@digitalocean.pts/0] ~/letsencrypt % uname -a
FreeBSD digitalocean.gehaowu.com 10.2-RELEASE FreeBSD 10.2-RELEASE #0 r286666: Wed Aug 12 15:26:37 UTC 2015 root@releng1.nyi.freebsd.org:/usr/obj/usr/src/sys/GENERIC amd64
[ghw@digitalocean.pts/0] ~/letsencrypt %