Hostname SSL with Letsencrypt, can't renew certificate

Hi All,

I have installed on my CentOSv6 with Apache the let's encrypt for the server, it works fine, but I can't renew it 

Used these instructions in December last year....  http://wiki.centos-webpanel.com/hostname-ssl-with-letsencrypt

Error:

The following certs could not be renewed:
  /etc/letsencrypt/live/sub.domain.com/fullchain.pem (failure)
IMPORTANT NOTES:
 - The following errors were reported by the server:

   Domain: sub.domain.com
   Type:   unauthorized
   Detail: Invalid response from
   http://sub.domain.com/.well-known/acme-challenge/UcnoQ8dI8D6PsGIMEpcvwTyPQL1ImGopjQqAsl0PBao:
   "
Not Found

Any ideas?