Hello!
Please have a look at your files and folders permissions.
I have this exactly problem in the past and I solve runing the following command at the webserver directory:
chown XXXXXX:XXXXXX . -R
find . -type d -exec chmod 755 {} \;
find . -type f -exec chmod 644 {} \;
PS: Please change the XXXXXX acording to your setup.
Best regards,