Try to either uninstall & reinstall then follow the steps I followed to create the new stuff.
If you can't do this because of user stats, then you must extract the INSERT INTO's from the /install/rpg_mysql-schema.php
What I stored in those tables are... well basically what the table names would indicate. But I can tell you that without proper info and relations between tables, bad things will start to happen even if this issue goes away
Btw, I just tested creating a new Class and making it "Blade User", and I could still have the item added to my inventory.