user@val:~$ sudo mv /etc/php5/conf.d/curl.ini /etc/php5/conf.d/z_curl.ini
First check if the web server is working.
Check that PHP is working. Create a foo.php script containing <?php phpinfo(); ?> to debug PHP configuration.
Next make sure you serve the YK-VAL code under the URL you want, and that accesssing the URL reaches the YK-VAL code. PHP error log in the file set by php.ini error_log, by default /var/log/apache2/error.log. Database errors will also be logged into it.
The database needs to be started. Make sure you can access it and the tables.
If ykval-export crashes, you may be running into a compatibility problem between PHP, curl and libpq. See http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=411982 for more information. The workaround is simple:
user@val:~$ sudo mv /etc/php5/conf.d/curl.ini /etc/php5/conf.d/z_curl.ini