[Lynne]

Try disabling your modifications/plugins and see if you still have this problem after manually running one of the jobs.
Note: To temporarily disable the plugin system, edit includes/config.php and add this line right under <?php

PHP Code:

define('DISABLE_HOOKS', true); 


If so, Create a new style with no parent:

• Styles & Templates > Style Manager > Add New Style
• Parent Style: No Parent Style
• Title: Default vBulletin
• Allow User Selection: Yes
• Save

Set this as the default in AdminCP > Settings > Options > Styles & Languages > Set Default Style. Then manually run one task and then browse the site using that totally default vbulletin style and see if the jobs are running.

If that doesn't fix it, a link to your site, running the default style/no mods, would help.