Add to the file, between <VirtualHost>...</VirtualHost>:
<Directory /data/sites/dev.domain.com/www/public>
Order allow,deny
allow from all
</Directory>
Make sure you have NameVirtualHost *:80 somewhere before this file is loaded. (You can stick it just before <VirtualHost *:80> to be sure.)
EDIT 2: Make sure you sudo a2ensite config_file config_file is the file that contains the <VirtualHost> block. Should be /etc/apache2/sites-available/dev.domain.com.conf and you should use sudo a2ensite dev.domain.com.conf
Make sure you sudo apahce2ctl restart
EDIT:
Regarding logs, not sure what your global conf is. You may need this within <VirtualHost>...</VirtualHost>:
ErrorLog /var/log/apache2/dev.domain.com-error.log
# Possible values include: debug, info, notice, warn, error, crit,
# alert, emerg.
LogLevel warn
CustomLog /var/log/apache2/dev.domain.com-access.log combined
If your page is a php page, then try to debug that page. Use the syslog() function to add debugging information and read the logs written by syslog to find out where it stops or where it is taking a lot of time to execute.
Better, you can use a PHP profiler or a PHP debugger.
Best Answer
Well, httpd is basically just the same as apache2 in most modern operating systems. Of course, you should check an actual version of Apache in your system because minor version numbers can (and will) differ.