Howdy, A couple of things...
First I would change your security - you have it set up so anyone can connect to your database from remote using your listed username and password for apache. Essentially the "%" allows for any host to connect...(Assuming you haven't blocked port or implemented other security).

Second - *IF* it is not a code problem, and because you are asking about what other tables might be involved, it just could be a mysql privilege issue. These are the typical relevant tables in database mysql

mysql> show tables;                              
+-----------------+
| Tables in mysql |
+-----------------+
| columns_priv    |
| db              |
| func            |
| host            |
| tables_priv     |
| user            |
+-----------------+
6 rows in set (0.00 sec)
[download]

For a look at the mysql docs on priviledges.. http://www.mysql.com/doc/P/r/Privilege_system.html

Specifically, look at your db table, which contains the priviledges based on a combination of user/host/database.

Also, if you post some code I'm sure it would help everyone be more helpful..:)

EEjack