blank page after an avatar plugin install

I've tried to install avatar plugin.

I've uploaded all the files and I modified the .htaccess file and now the site doesn't work anymore. At the wpmu address is a blank page. I restored the old .htaccess file but no change. I tried many tutorials/fix for this kind of problem. Nothing doesn't apparently work.

Please somebody from here if you know the issue.

The site is peblog.net

the .htaccess file at the moment of writing:

RewriteEngine On
RewriteBase /</p>
<p>#uploaded files
RewriteRule ^(.*/)?files/$ index.php [L]
RewriteCond %{REQUEST_URI} !.*wp-content/plugins.*
RewriteRule ^(.*/)?files/(.*) wp-content/blogs.php?file=$2 [L]
RewriteRule ^(.*/)?avatar/(.*) wp-content/avatar.php?file=$2 [L]</p>
<p># add a trailing slash to /wp-admin
RewriteCond %{REQUEST_URI} ^.*/wp-admin$
RewriteRule ^(.+)$ $1/ [R=301,L]</p>
<p>RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule . - [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(wp-.*) $2 [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(.*\.php)$ $2 [L]
RewriteRule . index.php [L]</p>
<p><IfModule mod_security.c>
<Files async-upload.php>
SecFilterEngine Off
SecFilterScanPOST Off
</Files>
</IfModule>
`