Search Engine Friendly Vars

[fire_cracker]

I am working on implimenting a method so that I can use search engine friendly vars; however, I am getting an error 500 when I try to run the script. Any ideas why it is broken?

if (isset($_SERVER['PATH_INFO'])) { 
$vardata = explode('/', $_SERVER['PATH_INFO']);

$num_param = count($vardata);

if ($num_param % 2 == 0) {
$vardata[] = '';
$num_param++;
}

for ($i = 1; $i < $num_param; $i += 2) {
if (!empty($vardata[$i]) AND !empty($vardata[$i+1])) {
$$vardata[$i] = addslashes($vardata[$i+1]);
}
}
}