I tried using both W3 Total Cache and WP Super Cache and both make my site get a 403 with gtmetrix.com, Pingdom Tools, fetching the site as Google Bot. The site displays fine though, it's just the bots and metrics sites that get a 403.
When I deactivate both plugins, everything is fine.
I haven't been able to make this work with any of the solutions provided online (which are by now outdated).
This is my htaccess file: http://pastebin.com/b0uQD6aL
Hosting company: Site5.
Does anybody know how to fix this?