Try disabling your 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);
If so, try reuploading the member.php file (make sure it's a totally default one).
Create a new style with no parent - Styles & Templates > Style Manager > Add New Style > no parent - then browse the site using that totally default vbulletin style - do you still have the same problem?