the 500 error message is very vague, it really just means an error occurred, to determine the cause of the error, error reporting needs to be enabled.
edit the webassist/kfm/index page and add the following code at line 1:
<?php
error_reporting(E_ALL);
ini_set('display_errors','on');
?>
once we know what the error is, we will be able to troubleshoot the cause.