OpenX is comming with its own PEAR installation.
If your hosting company has preinstalled PEAR for you you might got the error
PHP Fatal error: Cannot redeclare _pear_call_destructors() (previously declared in /usr/share/php/PEAR.php:765) in /home/…/ads/openx-2.6.4/lib/pear/PEAR.php on line XXX
To solve this make .htaccess file in the webroot of OpenX – dont put the .htaccess in your web root. Here is the contents of .htaccess :
php_value include_path ".:/home/domains/guda/ads/a/lib/pear"
You must enable AllowOverride in your apache configuration
<Directory /home/domains/guda/cenite.com/openx_webroot> AllowOverride all </Directory> Ref: https://developer.openx.org/jira/browse/OX-1006