As we prepare for the update to MySQL 5.1, there is one major issue that could affect your site that is very easy to check. MySQL 5.1 only authenticates usernames up to 16 characters in length. cPanel has automatically limited MySQL username lengths to 16 characters for many years, so if you started a new account with us in the last 5 years, chances are you’re already covered. If you moved from another host, or used to use another control panel other than cPanel, you might have problems.
The good news is checking the length of your database username, and fixing it if needed, is very simple. All you need to do is log in to cPanel and click on the MySQL Databases button. Scroll down to the Current Databases section and look under the Users column. If any of the usernames are longer than 16 characters, create a new database user and give them access to that database. Then you need to update the configuration file of the script that you’re using.
In Joomla it’s the configuration.php file. In WordPress it’s the wp-config.php file. For other scripts, refer to their documentation or open a support ticket.