Did you add localhost (or % for anyone) to the access list? This should only be neccessary if the web server accessing the database is off the server, however you might check to make sure "localhost" is there either way, and also, trouble shoot it by adding the percent sign (% , used by MySQL as a wildard)
You have to allow external web servers to access your MySQL databases by adding their domain name to the list of hosts that are able to access databases on your web site. localhost stands for your own web server.
To add host access:
Click on the MySQL databases button on the home page.
Enter the domain name or IP number of the host that you wish to add in the Host field.
Click on the Add Host button.