For me running 6.4.2
Go to the admin panel and run the following sql command (always backup your database beforehand, although this is purely a read only query):
SELECT * FROM `w3t_Ratings`
(This assumes you did leave the default table prefix as w3t.)
The output table shows which user numbers rated which user number and what rating they gave. It also shows thread rates as well.
Just scroll through until you see the same number rating 1's for everyone.