Logging in as the apache user (www-data) is useful when trying to figure out permission denied errors. I always first check that I can access the files when I am logged in as that user. Unfortunately, with ubuntu 14.04, unlike 12.04, the www-data user is set to not allow login, so you need to run the command(s) below.
sudo sed -i s;www-data:x:33:33:www-data:/var/www:/usr/sbin/nologin;www-data:x:33:33:www-data:/var/www:/bin/bash; /etc/passwd sudo su su www-data