Enabled multisite, lost database connection

I successfully moved a blog from a blog subdirectory to the root. Everything was working fine.

Then I followed instructions for enabling multisite, but did nothing else.

I inserted the following code into config.php

// ** Multi-site settings ** //
define ('WP_ALLOW_MULTISITE',true);
define( 'MULTISITE', true );
define( 'SUBDOMAIN_INSTALL', false );
$base = '/';
define( 'DOMAIN_CURRENT_SITE', 'thedomain.net' );
define( 'PATH_CURRENT_SITE', '/' );
define( 'SITE_ID_CURRENT_SITE', 1 );
define( 'BLOG_ID_CURRENT_SITE', 1 );

My .htaccess file looks like this:

# BEGIN WordPress
<IfModule mod_rewrite.c>

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

# uploaded files
RewriteRule ^([_0-9a-zA-Z-]+/)?files/(.+) wp-includes/ms-files.php?file=$2 [L]

# add a trailing slash to /wp-admin
RewriteRule ^([_0-9a-zA-Z-]+/)?wp-admin$ $1wp-admin/ [R=301,L]

RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ - [L]
RewriteRule  ^[_0-9a-zA-Z-]+/(wp-(content|admin|includes).*) $1 [L]
RewriteRule  ^[_0-9a-zA-Z-]+/(.*\.php)$ $1 [L]
RewriteRule . index.php [L]

</IfModule>

# END WordPress

Now I get an “Error Establishing Database Connection” message.

I checked that the database has the correct tables. It does.

I “repaired” the database. (It didn’t need it.)

How can I re-connect the blog to the database without going back to single-site settings? (It works fine as a single site as soon as I remove the extra code)