Issue with multisite, mod_rewrite & htaccess

Hello,
I’m trying to use mod_rewrite caching on my WP-Multisite installation, and I have the following message:
Mod Rewrite rules cannot be updated!

When I open up my htaccess file…everything between # BEGIN WPSuperCache and # END WPSuperCache looks fine.

Directly after that is my BEGIN & END WordPress…but there isn’t anything in-between the BEGIN/END. Should there be?

My permalink structure is working on the front-end…
/blog/%year%/%monthnum%/%day%/%postname%/

Here’s the htacess code BEFORE the # BEGIN WPSuperCache…

RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]

# uploaded files
RewriteRule ^files/(.+) wp-includes/ms-files.php?file=$1 [L]

RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ - [L]
RewriteRule . index.php [L]

Honestly, I’m not entirely sure what those are for…

Any ideas?

Thanks,
Craig