Database admin user name and/or password is invalid (Error 1251: Client does not support authentication protocol requested by server; consider upgrading MySQL client).
MySQL 4.1 introduced a new password hashing algorithm that older versions of Apache (1.x) and PHP (3.x and 4.x) don't support. For more information about the new password hashing algorithm in MySQL, see http://dev.mysql.com/doc/mysql/en/old-client.html.
There are multiple ways to workaround the error that you're seeing, including upgrading pieces of the architecture, or modifying MySQL to utilize the old password hashing algorithm.
One quick workaround is to issue the following MySQL query:
SET PASSWORD FOR 'username'@'localhost' = OLD_PASSWORD('new_password_here');