 <p>I'm assuming that the version of mongo listed in phpinfo is 1.2 -- MongoClient class wasn't out until v1.3</p> <p>if so, you need to update mongodb to the newer version.</p> <p><a href="https://bugs.launchpad.net/ubuntu/+source/php-mongo/+bug/1096587" rel="nofollow">https://bugs.launchpad.net/ubuntu/+source/php-mongo/+bug/1096587</a></p>