As I asked here when you have a Main category selected the sidebar moves to the bottom of the page.
As suggestere here: How to fix a template bug?
I removed all vBulletin integration. And I checked the Header with the w3c validator for errors, which were not there.
The result was a blank page, which still showed the problem with the rightsidebar.
Screenshot, generated HTML code (with added PROBLEM comments) and a screenshot of the w3c validator are in the zip-file http://www.xs4all.nl/~vdlogt/RightSidebar.zip