Arras Theme Sidebar Problem

Hello,

I am using WP 2.9 and the Arras Theme 1.3.6 on
https://www.brueckenkopf-online.com/

On the main page and in the categories everything works fine. As soon as i am on single page view / read an article, the sidebar jumps below the main content and slightly to the right.

Here you can see what i mean
https://www.brueckenkopf-online.com/?p=11048&cpage=1#comment-10325
The error happens just at the single view on articles, not on pages or categories.

Any solutions for this?

thanks in advance & regards

Dennis