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 need be, you may have to set this style as the default for that section.
I've the correct permission and I've use the solution in quote but is the same: not is possible use the editor...