FULTEXT query error

I’m getting lots of this in my error log:

WordPress database error
Can’t find FULLTEXT index matching the column list for query

and then it spits out the query created by the sql method in the YARPP_Cache class.

It’s doing this on my live site, but not my dev site, which is running all the same stuff.

How would I deal with this?

http://wordpress.org/extend/plugins/yet-another-related-posts-plugin/