If you got this error message in your Apache error log, you could check if the reason of this is that it folder on which the server is trying get access is readable by Apache user (www-data in Ubuntu by default). In order to test this condition, you could try:
work as root user
#su – www-data
if you get “can’t cd to yourDirectory” or similar is due that Apache user can’t access to the file or directory.
See error log from console:
#tail -f /var/log/apache2/error.log