Had the same problem but I find my solution!
Because $_SERVER[‘DOCUMENT_ROOT’] is not suitable for my hosting (it linked to Apache root /usr/local/apache/htdocs)
So I edit plugin file avatars.php on line 683
// The web-server root directory. Used to create absolute paths.
$root = avatar_root();
to
$root = '/home/myhostfolder/public_html/';
My /avatars folder is in my wordpress folder root. And now it works pretty well!
