Same – In my case the .htaccess file was corrupt, as the blacklist was truncated – a quick but unsatisfactory solution is replacing the file with an older (working) one by FTP
# BEGIN Ban Users
# Begin HackRepair.com Blacklist
RewriteEngine on
RewriteCond %{HTTP_USER_AGENT} ^Acunetix [NC,OR]
<snip apx 36 correct lines>
RewriteCond %{HTTP_USER_AGENT} ^Grafula [NC,OR]
RewriteCond %{HTTP_USE