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/>
      AllowOverride all