[Lynne]

Can we get a link?

Have you tried disabling your plugins via the config.php file?
Note: To temporarily disable the plugin system, edit includes/config.php and add this line right under <?php

PHP Code:

define('DISABLE_HOOKS', true); 


Does this happen on a default style?
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 go to Maintenance > Clear System Cache. Then browse the site using that totally default vbulletin style - do you still have the same problem?

Are all your files default?
Check maintenance > diagnostics > suspect file versions and see if any are listed as not containing expected contents.