Hi Emre,
I use WP Fastest Cache on a dozen sites of mine and have encountered an error after changing themes yesterday. Unitedfireandwater dot com used WP Fastest Cache prior to changing themes, but now I get an htaaccess error when caching. Thru FileZilla, I made htaaccess writeable, tried caching and was given a 500 error. All of my sites "hide" their public HTML folders, but I'm only experiencing these errors on this domain. May I email you more info? This site has PPC campaigns pushed to it, and I need to get it running smoothly as soon as possible. [Current load time is nearly 1 minute].
Thanks!