When you are upgrading MySQL from MySQL 3 or MySQL 4.0 to MySQL 4.1, you may find this error message
mysql_connect(): Client does not support authentication protocol
So, what should we do?
If, you have a lot of application then you may add the following statement to the [mysqld] section on MySQL configuration file (my.cnf)
Then, all of your application will be working like your MySQL prior plus you can maximize the new features on MySQL 4.1.