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);
Sorry to res an old thread, but I am also having this issue.
Scheduled tasks won't run on their own. I keep having to delete the vb_session periodically.
The footer is intact.
I have tried adding the PHP code that you mentioned to test disabling plugins, but it failed due to the fact that I'm using vB Advanced (I didn't consider that =_=).
This issue has been going on for some time now. I really need to find how to fix this.
It was just.... random.