Side note: You have this link just before your closing that is not going anywhere:
As for the site, it looks like some of the floats are doing some wild things. I noticed that your #wrapper has a fixed height, this is a pretty big no-no. What if the content needs to be taller than that? Same thing with the sidebar.
The error is probably occurring because you are using HTML5 elements and I don’t see you including anything to make it work in IE (like this http://code.google.com/p/html5shiv/ ).