WordPress 2.9 update puts WP DBmanager out of service
WordPress recently have released the WordPress 2.9 update to patch up and address few security and performance issues along with minor feature improvement.
However it has caused a major problem for regular bloggers, specifically speaking those who are pro-bloggers having large blogs with lots of activity.
One of the widely used and one of the must have plugin for wordpress is the WP-DBManager. A very popular plugin which helps to setup a system in which a blogger can automatically receive periodical database backup via email.
It seems ever since upgrade to WordPress 2.9, WP DBmanager have stopped working. In user report, it has came forward that for some reason with WordPress 2.9, the cron jobs are effected and not working properly.
So, if you are using the said plugin, then use any manual method to get your backup done.
Update (Jan 08, 2010)
After the release of WordPress 2.9.1, the said problem seems have solved. So update your WP installation and see if it has solved the issue for you or not.

Navjot Singh on December 31st, 2009
Fix is coming in WordPress 2.9.1. And if someone is facing problems, try patches from http://core.trac.wordpress.org/changeset/12473 or http://www.semiologic.com/2009/12/21/wp-2-9-three-bugs-and-how-to-fix-them/
or the easiest – add this in wp-config.php: define(‘ALTERNATE_WP_CRON’, true);
Strangely, WP-DB Manager is working perfectly for me and keeps sending me db by mail everyday with last one was send just 9 hours from now.
Maybe more of a webhost issue with cron?