I've been getting this error coming up in my system log. Having looked around for an answer, two things came up commonly: a problem with the spotlight database(s), and permissions on those folders.
Well, I played with permissions and even deleted some of the folders in question to see if they would be re-created properly. I think that was a mistake, there were odd side effects, so I tried my best to restore the folders to the way they had been previously.
Also, resetting MDS didn't help much. Most recently the error comes up when Outlook refuses to get my mail properly.
It's also always followed by Quicklook-related errors as well.