Multisite won't work

I am trying to enable WordPress Multi-Site on my blog running WordPress 3.3.2. It is also running Buddypress 1.5.5. I tried to put the required code, define(‘WP_ALLOW_MULTISITE’, true);, into the WP-Config file, but whenever I do so I get the error message Warning: ftp_put() [function.ftp-put]: Can’t open that file: Permission denied in /home/files/public_html/1/includes/filesystem.inc.php on line 684 I checked and double checked, but the WP_allow_multisite is in the right place. Thanks in advance!