If I enter a search term in quotes on the bnipodcast.com site (for instance, "you never know whom they know", I get a 403 error:
You are not authorized to access the webpage at http://www.bnipodcast.com/?s=%22you+never+know+whom+they+know%22&x=0&y=0. You may need to sign in.
(I get the error whether or not I am signed in.)
Actually, this first happened on WordPress 3.4.2; I tried upgrading to see whether that would fix it.
I don't believe that I got this error before the most recent update to Relevanssi.
The site is hosted at 1and1, so the server is probably horrid, but search load is not heavy.