big problem

Hello,
i’ve posted the same topic but i’m unable solve my problem.
I will try to explain .
i use this configuration /

define(‘WP_DEBUG’, false);
define(‘SUNRISE’, ‘on’);
define( ‘MULTISITE’, true );
define( ‘SUBDOMAIN_INSTALL’, false );
$base = ‘/’;
define( ‘DOMAIN_CURRENT_SITE’, ‘www.maindomain.com’ );
define( ‘PATH_CURRENT_SITE’, ‘/’ );
define( ‘SITE_ID_CURRENT_SITE’, 17 );
define( ‘BLOG_ID_CURRENT_SITE’, 17);
define( ‘NOBLOGREDIRECT’, ” );

i use domain mapping.
everythings works good when i create a blog and and apply a new domain or a subdomain on this.
But when i want to create a subfolder domain. like :
https://www.mainsite.com/mynewblog/ when i reach this address i have the content of the main site. idem https://www.mainsite.com/mynewblog/wp-admin
the panel of main domain is shown.

So i don’t know what’s going on … i’ve tried multiple suggestion but nothing works.

Any help would very very appreciate !

_________
.htaccess
———
SetEnv PHP_VER 5
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).*) $2 [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(.*\.php)$ $2 [L]
RewriteRule . index.php [L]