Admin Life Errors, Fixes, and Encounters

Error in openx scripts maintenance.php

from time to time you'll see this error from openx maintenance. Anyone have any idea why this happens?

subject: Cron /usr/local/bin/php /usr/local/www/openx/scripts/maintenance/maintenance.php openx.domain.com

Body: /libexec/ld-elf.so.1: /usr/local/lib/php/20060613/xml.so: Undefined symbol "XML_ParserCreate_MM"