Mass Move Threads Failed
 

I used the mass move threads option to move existing threads from one forum into a new forum. The process seemed to work fine because I saw that the threads had disappeared from the old forum. I then deleted the old forums from the forum manager page. That's when I noticed that the threads never really moved to the new forums because after running the Update Counter script my thread count dropped dramatically. I then checked my database and it seemed to have removed all of the old forum threads. What could I have done wrong in this situation so that I don't repeat it again?