So today I was getting impatient with some of the load times on SCCAForums.com, so I decided to run the SQL profiler on the database to see if there were any suggested improvements to speed it up.
I ran the tuning wizard and it came up with a suggest that would be a 93% improvement, sold, lets run the script!
Fast forward, an hour later, when I go to make a post on the server and boom it fails. WTF? "Hey Dave, can you post and see if my ban on your account works". He gets the same error.
Not good. Anyways, SQL server's tuning wizard created a view, and when applying an index to that view it setup a requirement for ARITHABORT ON to be set when inserting into the cs_posts table.
It took me a while to fix it, but I think everything is back up and running now. I removed the index on the view that was created :(
Lesson learned, don't just execute random SQL on your database, even if SQL server suggested it!