You tried to access MySQL with an old MySQL client library. The version of your MySQL client library can be checked in your phpinfo() output. In general, it should have at least the same minor version as your server - as mentioned in FAQ 1.17.

This problem is generally caused by using MySQL version 4.1 or newer. MySQL changed the authentication hash and your PHP is trying to use the old method. The proper solution is to use the mysqli extension with the proper client library to match...