No change to menus after enabling multisite

OK, I’ve tried really hard to find a solution by reading previous posts but I just can’t find one. It feels to me like I’ve tried everything but of course I haven’t so please bear with me if (as I hope) the solution is staring me in the face.

I have the following in the .htaccess file:

# BEGIN WordPress

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]

# END WordPress

I have added the following line to my wp-config.php file:

define('WP_ALLOW_MULTISITE', true);

I have placed this line in several places in the wp-config.php file (top, middle, bottom) while trying to get it to work.

The result is that I see NO new menu for Network under the tools menu, and if I go to mysite.com/wp-admin/network/ I get the “You do not have sufficient permissions to access this page.” message.

Has anyone found a common solution to this problem. What else could I try?

Thank you