Blocking spammers with mod_rewrite

[Perl]

Hey i used this but when i try to use any Ajax related work and try to move / prune any posts or even try to make new posts manually

Its says

406 Not Acceptable

An appropriate representation of the requested resource /index.php could not be found on this server.

Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.

Any help ?? FYI I use IPB 3.1.4

Tested few things it only occurs when you put last 3 lines

<IfModule rewrite_module>
RewriteEngine On
RewriteCond %{SERVER_PROTOCOL} ^(HTTP/1.0)
RewriteCond %{REQUEST_METHOD} ^(POST)
RewriteRule .* - [R=406]
</IfModule>

Any solution ?