IE CSS, I can’t find what’s causing the problem…

Hello all, I hope someone might be kind enough to have a quick peek at a site I just had go live, and ferret out what the problem is.

I’ve been staring at the code for hours and it’s all dancing in front of my eyes, I suspect it’s a silly thing missing somewhere or other, but I’m missing it entirely ??

In FF, the site works fine. In IE, the site also works fine, mostly! The design is a two column setup, with the sidebar appearing on the left of the main content. I use CSS to position them, in the source the sidebar comes after the text.

There are some pages where the sidebar is pushed below the content. Were it happening on every page, I’d question my CSS, but it’s not. So I’m thinking, it’s got to be something in the content that is causing conflict, but I can’t see what it might be.

The site is: https://ieccil.org
The offending pages are:
https://ieccil.org/disability-and-independent-living/independent-living-history/
https://ieccil.org/contact/
https://ieccil.org/sitemap/

I am unable to replicate the drop of the sidebar on both /contact and /sitemap but these were reported by two different individuals looking at the site (IE6).

I’m NOT worried about IE7 at this point, but would like to figure out the issue.

Please note that both the html and css validate.

Thanks for any and all assistance.