Force lowercase .htaccess

RewriteEngine On
RewriteMap  lc int:tolower
RewriteCond %{REQUEST_URI} [A-Z]
RewriteRule (.*) ${lc:$1} [R=301,L]

/home/public_html/.htaccess: RewriteMap not allowed here
[Mon Jul 18 10:33:06 2011] [alert] [client *.*.*.*] /home/public_html/.htaccess: RewriteMap not allowed here

$url = $_SERVER['REQUEST_URI'];
$pattern = '/([A-Z]+)/';

if(preg_match($pattern, $url)) {
    $new_url = strtolower($url);

    Header( 'HTTP/1.1 301 Moved Permanently' );
    Header( 'Location: ' . $new_url );
    exit;
}

// your code here