MultiSite subdirectory admin panel issue (redirect loop)

Dear Ron,

We had a working MU install of three sites.

It was set up like:
konferenciak.hu (main site)
konferenciak.hu/wellnessonline.hu (subsite 1)
konferenciak.hu/holidaytippek.hu (subsite 2)

We’d successfully installed your MU Domain Mapping plugin to map the subsites to new domains, but we’ve faced some problems which we can’t find the solution for. We would like to ask you to help us with your thoughts:

The biggest problem is that we can only access the main site’s admin backend, the subsites’ backend is not accessible, as every login attempt is halts with a REDIRECT_LOOP message.

Do you have any idea what might cause this problem?

Our htaccess is as follows (in case it is the cause you might spot the error in there):

RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ – [L]
# uploaded .les
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]

Thanks in advance,
Istvan

http://ww.wp.xz.cn/extend/plugins/wordpress-mu-domain-mapping/