letsencrypt not creating acme-challenge

letsencrypt not creating acme-challenge

Just following the simple instructions here (Debian 7 Wheezy with Nginx 1.8.x)
https://www.digitalocean.com/community/tutorials/how-to-secure-nginx-with-let-s-encrypt-on-ubuntu-14-04

./letsencrypt-auto certonly -a webroot --webroot-path=/var/www/html -d sub.domain.com

I see it creating the folder .well_known (under /var/www/html) but it 
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