problem with clean url - duplicate path and other strange issues

Hi all!
I've a serius problem with clean url's.
When I run the clean url test, theme was lost, with url http://www.site.com/admin/settings/clean-urls
Enabling clean url at this point, click on "save configuration", and the "administration theme" page is loaded, with url http://www.site.com/admin/settings/admin/settings/clean-urls

Then, if i click on "home" in the breadcrumb, page rimains the same (admin theme) and the url is http://www.site.com/admin/settings/admin/

If I click on "save configuration", url becomes http://www.site.com/admin/settings/admin/settings/admin/settings/admin/s...
and so on....

this is my .htaccess

#
# Apache/PHP/Drupal settings:
#

# Protect files and directories from prying eyes.

Order allow,deny

# Don't show directory listings for URLs which map to a directory.
Options -Indexes

# Follow symbolic links in this directory.
Options +FollowSymLinks

# Customized error messages.
ErrorDocument 404 /index.php

# Set the default handler.
DirectoryIndex index.php

# Override PHP settings. More in sites/default/settings.php
# but the following cannot be changed at runtime.

# PHP 4, Apache 1.

php_value magic_quotes_gpc 0
php_value register_globals 0
php_value session.auto_start 0

# PHP 4, Apache 2.

php_value magic_quotes_gpc 0
php_value register_globals 0
php_value session.auto_start 0

# PHP 5, Apache 1 and 2.

php_value magic_quotes_gpc 0
php_value register_globals 0
php_value session.auto_start 0

# Requires mod_expires to be enabled.

# Enable expirations.
ExpiresActive On
# Cache all files for 2 weeks after access (A).
ExpiresDefault A1209600
# Do not cache dynamically generated pages.
ExpiresByType text/html A1

# Various rewrite rules.

RewriteEngine on

# If your site can be accessed both with and without the prefix www. you
# can use one of the following settings to force user to use only one option:
#
# If you want the site to be accessed WITH the www. only, adapt and
# uncomment the following:
# RewriteCond %{HTTP_HOST} ^example\.com$ [NC]
# RewriteRule .* http://www.example.com/ [L,R=301]
#
# If you want the site to be accessed only WITHOUT the www. prefix, adapt
# and uncomment the following:
# RewriteCond %{HTTP_HOST} ^www\.example\.com$ [NC]
# RewriteRule .* http://example.com/ [L,R=301]

# Modify the RewriteBase if you are using Drupal in a subdirectory and
# the rewrite rules are not working properly.
#RewriteBase /

# Rewrite old-style URLs of the form 'node.php?id=x'.
#RewriteCond %{REQUEST_FILENAME} !-f
#RewriteCond %{REQUEST_FILENAME} !-d
#RewriteCond %{QUERY_STRING} ^id=([^&]+)$
#RewriteRule node.php index.php?q=node/view/%1 [L]

# Rewrite old-style URLs of the form 'module.php?mod=x'.
#RewriteCond %{REQUEST_FILENAME} !-f
#RewriteCond %{REQUEST_FILENAME} !-d
#RewriteCond %{QUERY_STRING} ^mod=([^&]+)$
#RewriteRule module.php index.php?q=%1 [L]

# Rewrite current-style URLs of the form 'index.php?q=x'.
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ index.php?q=$1 [L,QSA]

# $Id: .htaccess,v 1.81 2007/01/09 09:27:10 dries Exp $

uncomment rewritebase does not change anything.

Please help!!!