First try to disable all mods by "Disabling Hooks" and see if you still have the problem.
Instructions here:
http://www.vbulletin.com/forum/showt...ystem-globally
If you still have a problem try it using the default vBulletin style. To use the default style in your style manager in admin cp, make a new style with no parent.
If after both of these running vbulletin with no mods and using the default style you still have the problem I would post on vbulletin.com for official support.