Multisite installation in 1and1 gets Error 500

I have installed WordPress 3.2.1 without problems in 1and1, but afterwards, when trying to make a multisite with subdirectories, it gave me an error 500 and stopped working. If I remove the .htaccess file it works again, but I cannot work in multisite mode that way.

I just followed the steps in the Network install in Worpress, creating the blogs.dir directory with 777 mode, and adding the lines in wp-config.php and .htaccess.

I looked for solutions in Google, and found that I could add these lines at the beginning of my .htaccess file, but they did not work either:

Options All -Indexes
Options -MultiViews
AddType x-mapp-php5 .php
AddHandler x-mapp-php5 .php

It was also recommended to add a php.ini file with these lines

memory=64MB;
upload_max_filesize=64M;
post_max_size=64M;

Which did not work either.

I also looked for info on how to fix this in ths forum, but found nothing, and of course, I called the 1and1 support, but they told me that, since it was an external app, I should find the solution myself.

I am desperate about this and have been trying to fix it for days. Anyone can help me to fix this?

Here is my .htaccess file:

# Added for 1and1
Options All -Indexes
Options -MultiViews
AddType x-mapp-php5 .php
AddHandler x-mapp-php5 .php
# RewriteEngine On
# RewriteBase /

# BEGIN WordPress
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]
# END WordPress