how many users do you have? Could you delete them all except for admin and clean out all the rows in wp_usermeta table except thoes associated with the ADMIN user?
For each user there is one row in the wp_user table and each user has an ID with admin being number 1. In the wp_usermeta table there can be many rows for each user in the wp_user table. Each row has it's unique UMETA_ID and a field called USER_ID that matches the ID field in the wp_user table.
You can have one user with 5 rows in the wp_usermeta table, while another has 17 rows associated with it. It all depends on what has happened with that user.