onChange="submit()" for select only works once

The title pretty much says it all. I am creating a page for a restuarant for their comments.
http://www.eatatwades.com/dyncomm.php
The last select box should reload the page with the correct type of comments.
My problem is that it works perfectly the first time, but not the second. I get a javascript error saying that object doesn't support property or method. There is only one form on the page, the extra stuff is loaded via php include(). The .inc files contain only html. Other than the extra html,nothing is changed.
Any thoughts? I'm stumped.

Thanks
Jason