mysqlnd cannot connect to MySQL 4.1+ using the old insecure authentication. Please use an administration tool to reset your password with the command SET PASSWORD = PASSWORD(‘your_existing_password’). This will store a new, and more secure, hash value in mysql.user. If this user is used in other scripts executed by PHP 5.2 or earlier you might need to remove the old-passwords flag from your my.cnf file
有可能是PHP使用新版連線方式，而MySQL帳號密碼編碼是使用舊版Hash方式，長度只有16(新版是41)，導致Hash值不對所以無法登入。
