a 500 error message is very vague and tough to troubleshoot.
If you are using E to test, try using a different browser, it may show a more informative error message.
It also may be that error reporting is turned off in php, try adding the following to line of the page you are getting the error on to turn error reporting on:
<?php
error_reporting(E_ALL);
ini_set('display_errors','on');
?>