This usually means that your database user name or password is either incorrect, or not established yet. If you are using a user name and password that is different from your hosting user name and password, make sure that you have added that user name and password that is set in your stconfig.php file (in the secure directory) into your control panel.

Also check to ensure that your user name is associated with the database. After adding a mySQL user and password, make sure to click "Add User to Database" to associate that user with the database.

Check your mySQL user name. Even though you can create a user name with more than 8 characters, when you call it in your config file, you will only need the first 8 characters. So if your user name is mysite_cataloguser, you will use mysite_catalogu in the stconfig.php file.

Finally, check your mySQL user name prefixes. On some servers (like Alabanza hosts and cPanel servers), you will need to prefix your mySQL user name with your hosting user name. So if you create the user name "catuser", your mySQL user name may be "yoursite_catuser".