After running this...
SQL Query
SELECT Count( * ) AS UserPosts, POST_POSTER_NAME 
FROM ubbt_POSTS 
WHERE POST_POSTED_TIME > UNIX_TIMESTAMP( CURRENT_DATE ) -86400 *60 
GROUP BY POST_POSTER_NAME 
ORDER BY UserPosts DESC
I notice in one case...

UserPosts=2 POST_POSTER_NAME =

i.e. blank / empty.

Any thoughts on why this could be?

(I've deleted one user but he had many more posts than that.)