Help WP Multisite susDIRECTORY (wp installed in subfolder)

Hi i need help!

I have installed a WP Multi Site subDIRECTORY instance installed in a folder : /wrdprss

when i enter a (non existing) url:
mydomain.tld/blabla
i get a tab in my browser (PAGE NOT FOUND)
while the rendered page shows a WP PAGE (theme is Twenty Twelve)

This is somewhat embarrassing, isn’t it?
It seems we can’t find what you’re looking for. Perhaps searching can help.

This is my .htaccess (in the html root folder)

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).*) wrdprss/$2 [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(.*\.php)$ wrdprss/$2 [L]
RewriteRule . index.php [L]

And this is part of my wp-config.php file

/* Multisite */
define(‘WP_ALLOW_MULTISITE’, true);
define(‘MULTISITE’, true);
define(‘SUBDOMAIN_INSTALL’, false);
define(‘DOMAIN_CURRENT_SITE’, ‘mydomain.tld’);
define(‘PATH_CURRENT_SITE’, ‘/’);
define(‘SITE_ID_CURRENT_SITE’, 1);
define(‘BLOG_ID_CURRENT_SITE’, 1);

define(‘ADMIN_COOKIE_PATH’, ‘/’);
define(‘COOKIE_DOMAIN’, ”);
define(‘COOKIEPATH’, ”);
define(‘SITECOOKIEPATH’, ”);

Thanx for any you could help me!

btw:
other created (sub)sites works
(well at least no problems found til now!)