I would check your error_logs (if you don't know where they are, ask your host) first since that is a server error. Hopefully something is in there.
You can also try going into debug mode to see what the actual error is.
To enable debug mode edit the /config.php file and change:
Code:
$config['debug'] = false;
To:
Code:
$config['debug'] = true;
Then edit the /core/includes/config.php file and change:
Code:
// $config['Misc']['debug'] = true;
To:
Code:
$config['Misc']['debug'] = true;
To set that up for only your IP address (replace xxx.xxx.xxx.xxx with your IP), put these lines around the code:
Code:
if($_SERVER['REMOTE_ADDR'] == "xxx.xxx.xxx.xxx") {
CODE HERE
}