Verify your assumptions about file permissions by testing them!
www-data comes to mind. Will Apache be able to read that folder?
sudo -u <user> test -r </location/to/test>sudo's -u allows you to specify a specific user (instead of the usual root). Then run test -r which determines if the passed file exists and can be read.
NB. If your terminal isn't setup to display return codes then you can run the following (example with www-data):
sudo -u www-data test -r /var/data; echo $?$? holds whatever the last command returned. Generally, 0 => Success, Not 0 => Failure.