[Lynne]

I can see the error when clicking on the second link. A non-logged in user should just get a screen to login.

Did you ever try disabling your plugins to see if the error goes away? Or try using a default style to see if you still get the error?

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
Then browse the site using that totally default vbulletin style - do you still have the same problem?

If it is still happening - Try disabling your modifications/plugins and see if you still have this problem.
Note: To temporarily disable the plugin system, edit config.php and add this line right under <?php

PHP Code:

define('DISABLE_HOOKS', true); 


Don't forget that for vbseo, disabling the modification means to also get rid of anything extra you added to your htaccess file.