Frankly, I have no idea.It has been brought to my attention that my host had the server down for maintenance yesterday, so this must be a mistake on their part. Judging from the MySQL error message, the table keeping track of the NEW labels broke.
Fixing it was simple, I just removed the old table and created a new one. Due to this, every forum has basically been marked read for every user. I figured it wasn't much of a loss.