Someone else posted this same problem in this forum a few months back. Unfortunately, I don't think anyone had a good answer. You may try and reply to that post to see if the original poster figured it out.
I think it has something to do with IE7 incorrecty parsing the page. My only advice was to check for wierd characters or extra spaces in the code.
You may have to try some thing like this:
to try and track exactly where the problem is. Of course you would have to start at the top of your page and keep moving the code down until you get the same Bad Request error.