I'll need FTP access in order to debug this. It could be a missing file that wasn't uploaded or a syntax error, but it would be too hard to find without active debugging.
You could try adding this to the top of the page:
<?php
ini_set("error_reporting",1);
?>
That is the first thing I would try. It should give you a more readable error that you might be able to figure out how to fix instead of the general 500 error.