I've got ratings activated (but not ratings by guests) on my most recent install. While I haven't used them, I didn't get any such error turning them on. Hang on...yeah, I can in fact set ratings, too.

I agree with the previous poster that that pattern of error messages matches some protection issues (which I just had on photo files in galleries/). In my precise case (host is Dreamhost) stuff run in and read/written by the PHP code can be readable (or writable if it's written) only by my user, but stuff served directly out of Apache (or whatever other web server) has to be world-read; so a default install doesn't set things up exactly right in that situation.  (The situation is PHP being run via FCGI, but a big central Apache install; this is likely on commercial shared hosting, much less likely on private servers.)

But...my install with default protections has working rating, and didn't crash when I turned ratings on, so perhaps that's a complete red herring.