One of 2 things I know of can cause this.
1. You gave yourself an Item that is not supported in the game anymore.
2. Your sql file are corrupted and needs repaired...Go into your mysql and go to the tables for the game and right click on them and go down to where it say's Maintain Tables and then click repair that should fix the problem if not go through your tables and find the item you gave yourself in the item.sql and delelte it.