Try creating a new default style, now test a post in that style, does the error remain?
http://www.vbulletin.com/forum/showt...le-to-Download
As a rule of thumb, it's never advised to upgrade a live/production site with a Beta version, always retain the latest stable version on your live site and create a test site to see how upgrades perform.
http://www.vbulletin.com/forum/conte...ng-A-Test-Site