Disable comments > Problem with sidebar

there are two closing </div> missing after the comments tests; in the linked site.
i assume that these are in the code that does not get used when comments are disabled (comment forms etc.)

have a very close look at comments.php of your theme and see if you can identify and relocate these closing divs.

if you would like help, you could paste the code of comments.php into a http://wordpress.pastebin.com/ and post the link to it here. someone might have a look at it and might be able to suggest a solution.