I am using the default config while adding the specific directory with nginx installed on my ubuntu 12.04 machine.
server {
#listen 80; ## listen
Nginx need to have +x access on all directories leading to the site's root directory.
Ensure you have +x on all of the directories in the path leading to the site's root. For example, if the site root is /home/username/siteroot:
chmod +x /home/
chmod +x /home/username
chmod +x /home/username/siteroot